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  <title>P0323R9: std::expected</title>
<style data-fill-with="stylesheet">/******************************************************************************
 *                   Style sheet for the W3C specifications                   *
 *
 * Special classes handled by this style sheet include:
 *
 * Indices
 *   - .toc for the Table of Contents (<ol class="toc">)
 *     + <span class="secno"> for the section numbers
 *   - #toc for the Table of Contents (<nav id="toc">)
 *   - ul.index for Indices (<a href="#ref">term</a><span>, in §N.M</span>)
 *   - table.index for Index Tables (e.g. for properties or elements)
 *
 * Structural Markup
 *   - table.data for general data tables
 *     -> use 'scope' attribute, <colgroup>, <thead>, and <tbody> for best results !
 *     -> use <table class='complex data'> for extra-complex tables
 *     -> use <td class='long'> for paragraph-length cell content
 *     -> use <td class='pre'> when manual line breaks/indentation would help readability
 *   - dl.switch for switch statements
 *   - ol.algorithm for algorithms (helps to visualize nesting)
 *   - .figure and .caption (HTML4) and figure and figcaption (HTML5)
 *     -> .sidefigure for right-floated figures
 *   - ins/del
 *
 * Code
 *   - pre and code
 *
 * Special Sections
 *   - .note       for informative notes             (div, p, span, aside, details)
 *   - .example    for informative examples          (div, p, pre, span)
 *   - .issue      for issues                        (div, p, span)
 *   - .assertion  for assertions                    (div, p, span)
 *   - .advisement for loud normative statements     (div, p, strong)
 *   - .annoying-warning for spec obsoletion notices (div, aside, details)
 *
 * Definition Boxes
 *   - pre.def   for WebIDL definitions
 *   - table.def for tables that define other entities (e.g. CSS properties)
 *   - dl.def    for definition lists that define other entitles (e.g. HTML elements)
 *
 * Numbering
 *   - .secno for section numbers in .toc and headings (<span class='secno'>3.2</span>)
 *   - .marker for source-inserted example/figure/issue numbers (<span class='marker'>Issue 4</span>)
 *   - ::before styled for CSS-generated issue/example/figure numbers:
 *     -> Documents wishing to use this only need to add
 *        figcaption::before,
 *        .caption::before { content: "Figure "  counter(figure) " ";  }
 *        .example::before { content: "Example " counter(example) " "; }
 *        .issue::before   { content: "Issue "   counter(issue) " ";   }
 *
 * Header Stuff (ignore, just don't conflict with these classes)
 *   - .head for the header
 *   - .copyright for the copyright
 *
 * Miscellaneous
 *   - .overlarge for things that should be as wide as possible, even if
 *     that overflows the body text area. This can be used on an item or
 *     on its container, depending on the effect desired.
 *     Note that this styling basically doesn't help at all when printing,
 *     since A4 paper isn't much wider than the max-width here.
 *     It's better to design things to fit into a narrower measure if possible.
 *   - js-added ToC jump links (see fixup.js)
 *
 ******************************************************************************/

/******************************************************************************/
/*                                   Body                                     */
/******************************************************************************/

	body {
		counter-reset: example figure issue;

		/* Layout */
		max-width: 50em;               /* limit line length to 50em for readability   */
		margin: 0 auto;                /* center text within page                     */
		padding: 1.6em 1.5em 2em 50px; /* assume 16px font size for downlevel clients */
		padding: 1.6em 1.5em 2em calc(26px + 1.5em); /* leave space for status flag     */

		/* Typography */
		line-height: 1.5;
		font-family: sans-serif;
		widows: 2;
		orphans: 2;
		word-wrap: break-word;
		overflow-wrap: break-word;
		hyphens: auto;

		/* Colors */
		color: black;
		background: white top left fixed no-repeat;
		background-size: 25px auto;
	}


/******************************************************************************/
/*                         Front Matter & Navigation                          */
/******************************************************************************/

/** Header ********************************************************************/

	div.head { margin-bottom: 1em }
	div.head hr { border-style: solid; }

	div.head h1 {
		font-weight: bold;
		margin: 0 0 .1em;
		font-size: 220%;
	}

	div.head h2 { margin-bottom: 1.5em;}

/** W3C Logo ******************************************************************/

	.head .logo {
		float: right;
		margin: 0.4rem 0 0.2rem .4rem;
	}

	.head img[src*="logos/W3C"] {
		display: block;
		border: solid #1a5e9a;
		border-width: .65rem .7rem .6rem;
		border-radius: .4rem;
		background: #1a5e9a;
		color: white;
		font-weight: bold;
	}

	.head a:hover > img[src*="logos/W3C"],
	.head a:focus > img[src*="logos/W3C"] {
		opacity: .8;
	}

	.head a:active > img[src*="logos/W3C"] {
		background: #c00;
		border-color: #c00;
	}

	/* see also additional rules in Link Styling section */

/** Copyright *****************************************************************/

	p.copyright,
	p.copyright small { font-size: small }

/** Back to Top / ToC Toggle **************************************************/

	@media print {
		#toc-nav {
			display: none;
		}
	}
	@media not print {
		#toc-nav {
			position: fixed;
			z-index: 2;
			bottom: 0; left: 0;
			margin: 0;
			min-width: 1.33em;
			border-top-right-radius: 2rem;
			box-shadow: 0 0 2px;
			font-size: 1.5em;
			color: black;
		}
		#toc-nav > a {
			display: block;
			white-space: nowrap;

			height: 1.33em;
			padding: .1em 0.3em;
			margin: 0;

			background: white;
			box-shadow: 0 0 2px;
			border: none;
			border-top-right-radius: 1.33em;
			background: white;
		}
		#toc-nav > #toc-jump {
			padding-bottom: 2em;
			margin-bottom: -1.9em;
		}

		#toc-nav > a:hover,
		#toc-nav > a:focus {
			background: #f8f8f8;
		}
		#toc-nav > a:not(:hover):not(:focus) {
			color: #707070;
		}

		/* statusbar gets in the way on keyboard focus; remove once browsers fix */
		#toc-nav > a[href="#toc"]:not(:hover):focus:last-child {
			padding-bottom: 1.5rem;
		}

		#toc-nav:not(:hover) > a:not(:focus) > span + span {
			/* Ideally this uses :focus-within on #toc-nav */
			display: none;
		}
		#toc-nav > a > span + span {
			padding-right: 0.2em;
		}

		#toc-toggle-inline {
			vertical-align: 0.05em;
			font-size: 80%;
			color: gray;
			color: hsla(203,20%,40%,.7);
			border-style: none;
			background: transparent;
			position: relative;
		}
		#toc-toggle-inline:hover:not(:active),
		#toc-toggle-inline:focus:not(:active) {
			text-shadow: 1px 1px silver;
			top: -1px;
			left: -1px;
		}

		#toc-nav :active {
			color: #C00;
		}
	}

/** ToC Sidebar ***************************************************************/

	/* Floating sidebar */
	@media screen {
		body.toc-sidebar #toc {
			position: fixed;
			top: 0; bottom: 0;
			left: 0;
			width: 23.5em;
			max-width: 80%;
			max-width: calc(100% - 2em - 26px);
			overflow: auto;
			padding: 0 1em;
			padding-left: 42px;
			padding-left: calc(1em + 26px);
			background: inherit;
			background-color: #f7f8f9;
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) inset;
		}
		body.toc-sidebar #toc h2 {
			margin-top: .8rem;
			font-variant: small-caps;
			font-variant: all-small-caps;
			text-transform: lowercase;
			font-weight: bold;
			color: gray;
			color: hsla(203,20%,40%,.7);
		}
		body.toc-sidebar #toc-jump:not(:focus) {
			width: 0;
			height: 0;
			padding: 0;
			position: absolute;
			overflow: hidden;
		}
	}
	/* Hide main scroller when only the ToC is visible anyway */
	@media screen and (max-width: 28em) {
		body.toc-sidebar {
			overflow: hidden;
		}
	}

	/* Sidebar with its own space */
	@media screen and (min-width: 78em) {
		body:not(.toc-inline) #toc {
			position: fixed;
			top: 0; bottom: 0;
			left: 0;
			width: 23.5em;
			overflow: auto;
			padding: 0 1em;
			padding-left: 42px;
			padding-left: calc(1em + 26px);
			background: inherit;
			background-color: #f7f8f9;
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) inset;
		}
		body:not(.toc-inline) #toc h2 {
			margin-top: .8rem;
			font-variant: small-caps;
			font-variant: all-small-caps;
			text-transform: lowercase;
			font-weight: bold;
			color: gray;
			color: hsla(203,20%,40%,.7);
		}

		body:not(.toc-inline) {
			padding-left: 29em;
		}
		/* See also Overflow section at the bottom */

		body:not(.toc-inline) #toc-jump:not(:focus) {
			width: 0;
			height: 0;
			padding: 0;
			position: absolute;
			overflow: hidden;
		}
	}
	@media screen and (min-width: 90em) {
		body:not(.toc-inline) {
			margin: 0 4em;
		}
	}

/******************************************************************************/
/*                                Sectioning                                  */
/******************************************************************************/

/** Headings ******************************************************************/

	h1, h2, h3, h4, h5, h6, dt {
		page-break-after: avoid;
		page-break-inside: avoid;
		font: 100% sans-serif;   /* Reset all font styling to clear out UA styles */
		font-family: inherit;    /* Inherit the font family. */
		line-height: 1.2;        /* Keep wrapped headings compact */
		hyphens: manual;         /* Hyphenated headings look weird */
	}

	h2, h3, h4, h5, h6 {
		margin-top: 3rem;
	}

	h1, h2, h3 {
		color: #005A9C;
		background: transparent;
	}

	h1 { font-size: 170%; }
	h2 { font-size: 140%; }
	h3 { font-size: 120%; }
	h4 { font-weight: bold; }
	h5 { font-style: italic; }
	h6 { font-variant: small-caps; }
	dt { font-weight: bold; }

/** Subheadings ***************************************************************/

	h1 + h2,
	#subtitle {
		/* #subtitle is a subtitle in an H2 under the H1 */
		margin-top: 0;
	}
	h2 + h3,
	h3 + h4,
	h4 + h5,
	h5 + h6 {
		margin-top: 1.2em; /* = 1 x line-height */
	}

/** Section divider ***********************************************************/

	:not(.head) > hr {
		font-size: 1.5em;
		text-align: center;
		margin: 1em auto;
		height: auto;
		border: transparent solid 0;
		background: transparent;
	}
	:not(.head) > hr::before {
		content: "\2727\2003\2003\2727\2003\2003\2727";
	}

/******************************************************************************/
/*                            Paragraphs and Lists                            */
/******************************************************************************/

	p {
		margin: 1em 0;
	}

	dd > p:first-child,
	li > p:first-child {
		margin-top: 0;
	}

	ul, ol {
		margin-left: 0;
		padding-left: 2em;
	}

	li {
		margin: 0.25em 0 0.5em;
		padding: 0;
	}

	dl dd {
		margin: 0 0 .5em 2em;
	}

	.head dd + dd { /* compact for header */
		margin-top: -.5em;
	}

	/* Style for algorithms */
	ol.algorithm ol:not(.algorithm),
	.algorithm > ol ol:not(.algorithm) {
	 border-left: 0.5em solid #DEF;
	}

	/* Put nice boxes around each algorithm. */
	[data-algorithm]:not(.heading) {
	  padding: .5em;
	  border: thin solid #ddd; border-radius: .5em;
	  margin: .5em calc(-0.5em - 1px);
	}
	[data-algorithm]:not(.heading) > :first-child {
	  margin-top: 0;
	}
	[data-algorithm]:not(.heading) > :last-child {
	  margin-bottom: 0;
	}

	/* Style for switch/case <dl>s */
	dl.switch > dd > ol.only,
	dl.switch > dd > .only > ol {
	 margin-left: 0;
	}
	dl.switch > dd > ol.algorithm,
	dl.switch > dd > .algorithm > ol {
	 margin-left: -2em;
	}
	dl.switch {
	 padding-left: 2em;
	}
	dl.switch > dt {
	 text-indent: -1.5em;
	 margin-top: 1em;
	}
	dl.switch > dt + dt {
	 margin-top: 0;
	}
	dl.switch > dt::before {
	 content: '\21AA';
	 padding: 0 0.5em 0 0;
	 display: inline-block;
	 width: 1em;
	 text-align: right;
	 line-height: 0.5em;
	}

/** Terminology Markup ********************************************************/


/******************************************************************************/
/*                                 Inline Markup                              */
/******************************************************************************/

/** Terminology Markup ********************************************************/
	dfn   { /* Defining instance */
		font-weight: bolder;
	}
	a > i { /* Instance of term */
		font-style: normal;
	}
	dt dfn code, code.idl {
		font-size: medium;
	}
	dfn var {
		font-style: normal;
	}

/** Change Marking ************************************************************/

	del { color: red;  text-decoration: line-through; }
	ins { color: #080; text-decoration: underline;    }

/** Miscellaneous improvements to inline formatting ***************************/

	sup {
		vertical-align: super;
		font-size: 80%
	}

/******************************************************************************/
/*                                    Code                                    */
/******************************************************************************/

/** General monospace/pre rules ***********************************************/

	pre, code, samp {
		font-family: Menlo, Consolas, "DejaVu Sans Mono", Monaco, monospace;
		font-size: .9em;
		page-break-inside: avoid;
		hyphens: none;
		text-transform: none;
	}
	pre code,
	code code {
		font-size: 100%;
	}

	pre {
		margin-top: 1em;
		margin-bottom: 1em;
		overflow: auto;
	}

/** Inline Code fragments *****************************************************/

  /* Do something nice. */

/******************************************************************************/
/*                                    Links                                   */
/******************************************************************************/

/** General Hyperlinks ********************************************************/

	/* We hyperlink a lot, so make it less intrusive */
	a[href] {
		color: #034575;
		text-decoration: none;
		border-bottom: 1px solid #707070;
		/* Need a bit of extending for it to look okay */
		padding: 0 1px 0;
		margin: 0 -1px 0;
	}
	a:visited {
		border-bottom-color: #BBB;
	}

	/* Use distinguishing colors when user is interacting with the link */
	a[href]:focus,
	a[href]:hover {
		background: #f8f8f8;
		background: rgba(75%, 75%, 75%, .25);
		border-bottom-width: 3px;
		margin-bottom: -2px;
	}
	a[href]:active {
		color: #C00;
		border-color: #C00;
	}

	/* Backout above styling for W3C logo */
	.head .logo,
	.head .logo a {
		border: none;
		text-decoration: none;
		background: transparent;
	}

/******************************************************************************/
/*                                    Images                                  */
/******************************************************************************/

	img {
		border-style: none;
	}

	/* For autogen numbers, add
	   .caption::before, figcaption::before { content: "Figure " counter(figure) ". "; }
	*/

	figure, .figure, .sidefigure {
		page-break-inside: avoid;
		text-align: center;
		margin: 2.5em 0;
	}
	.figure img,    .sidefigure img,    figure img,
	.figure object, .sidefigure object, figure object {
		max-width: 100%;
		margin: auto;
	}
	.figure pre, .sidefigure pre, figure pre {
		text-align: left;
		display: table;
		margin: 1em auto;
	}
	.figure table, figure table {
		margin: auto;
	}
	@media screen and (min-width: 20em) {
		.sidefigure {
			float: right;
			width: 50%;
			margin: 0 0 0.5em 0.5em
		}
	}
	.caption, figcaption, caption {
		font-style: italic;
		font-size: 90%;
	}
	.caption::before, figcaption::before, figcaption > .marker {
		font-weight: bold;
	}
	.caption, figcaption {
		counter-increment: figure;
	}

	/* DL list is indented 2em, but figure inside it is not */
	dd > .figure, dd > figure { margin-left: -2em }

/******************************************************************************/
/*                             Colored Boxes                                  */
/******************************************************************************/

	.issue, .note, .example, .assertion, .advisement, blockquote {
		padding: .5em;
		border: .5em;
		border-left-style: solid;
		page-break-inside: avoid;
	}
	span.issue, span.note {
		padding: .1em .5em .15em;
		border-right-style: solid;
	}

	.issue,
	.note,
	.example,
	.advisement,
	.assertion,
	blockquote {
		margin: 1em auto;
	}
	.note  > p:first-child,
	.issue > p:first-child,
	blockquote > :first-child {
		margin-top: 0;
	}
	blockquote > :last-child {
		margin-bottom: 0;
	}

/** Blockquotes ***************************************************************/

	blockquote {
		border-color: silver;
	}

/** Open issue ****************************************************************/

	.issue {
		border-color: #E05252;
		background: #FBE9E9;
		counter-increment: issue;
		overflow: auto;
	}
	.issue::before, .issue > .marker {
		text-transform: uppercase;
		color: #AE1E1E;
		padding-right: 1em;
		text-transform: uppercase;
	}
	/* Add .issue::before { content: "Issue " counter(issue) " "; } for autogen numbers,
	   or use class="marker" to mark up the issue number in source. */

/** Example *******************************************************************/

	.example {
		border-color: #E0CB52;
		background: #FCFAEE;
		counter-increment: example;
		overflow: auto;
		clear: both;
	}
	.example::before, .example > .marker {
		text-transform: uppercase;
		color: #827017;
		min-width: 7.5em;
		display: block;
	}
	/* Add .example::before { content: "Example " counter(example) " "; } for autogen numbers,
	   or use class="marker" to mark up the example number in source. */

/** Non-normative Note ********************************************************/

	.note {
		border-color: #52E052;
		background: #E9FBE9;
		overflow: auto;
	}

	.note::before, .note > .marker,
	details.note > summary::before,
	details.note > summary > .marker {
		text-transform: uppercase;
		display: block;
		color: hsl(120, 70%, 30%);
	}
	/* Add .note::before { content: "Note"; } for autogen label,
	   or use class="marker" to mark up the label in source. */

	details.note > summary {
		display: block;
		color: hsl(120, 70%, 30%);
	}
	details.note[open] > summary {
		border-bottom: 1px silver solid;
	}

/** Assertion Box *************************************************************/
	/*  for assertions in algorithms */

	.assertion {
		border-color: #AAA;
		background: #EEE;
	}

/** Advisement Box ************************************************************/
	/*  for attention-grabbing normative statements */

	.advisement {
		border-color: orange;
		border-style: none solid;
		background: #FFEECC;
	}
	strong.advisement {
		display: block;
		text-align: center;
	}
	.advisement > .marker {
		color: #B35F00;
	}

/** Spec Obsoletion Notice ****************************************************/
	/* obnoxious obsoletion notice for older/abandoned specs. */

	details {
		display: block;
	}
	summary {
		font-weight: bolder;
	}

	.annoying-warning:not(details),
	details.annoying-warning:not([open]) > summary,
	details.annoying-warning[open] {
		background: #fdd;
		color: red;
		font-weight: bold;
		padding: .75em 1em;
		border: thick red;
		border-style: solid;
		border-radius: 1em;
	}
	.annoying-warning :last-child {
		margin-bottom: 0;
	}

@media not print {
	details.annoying-warning[open] {
		position: fixed;
		left: 1em;
		right: 1em;
		bottom: 1em;
		z-index: 1000;
	}
}

	details.annoying-warning:not([open]) > summary {
		text-align: center;
	}

/** Entity Definition Boxes ***************************************************/

	.def {
		padding: .5em 1em;
		background: #DEF;
		margin: 1.2em 0;
		border-left: 0.5em solid #8CCBF2;
	}

/******************************************************************************/
/*                                    Tables                                  */
/******************************************************************************/

	th, td {
		text-align: left;
		text-align: start;
	}

/** Property/Descriptor Definition Tables *************************************/

	table.def {
		/* inherits .def box styling, see above */
		width: 100%;
		border-spacing: 0;
	}

	table.def td,
	table.def th {
		padding: 0.5em;
		vertical-align: baseline;
		border-bottom: 1px solid #bbd7e9;
	}

	table.def > tbody > tr:last-child th,
	table.def > tbody > tr:last-child td {
		border-bottom: 0;
	}

	table.def th {
		font-style: italic;
		font-weight: normal;
		padding-left: 1em;
		width: 3em;
	}

	/* For when values are extra-complex and need formatting for readability */
	table td.pre {
		white-space: pre-wrap;
	}

	/* A footnote at the bottom of a def table */
	table.def           td.footnote {
		padding-top: 0.6em;
	}
	table.def           td.footnote::before {
		content: " ";
		display: block;
		height: 0.6em;
		width: 4em;
		border-top: thin solid;
	}

/** Data tables (and properly marked-up index tables) *************************/
	/*
		 <table class="data"> highlights structural relationships in a table
		 when correct markup is used (e.g. thead/tbody, th vs. td, scope attribute)

		 Use class="complex data" for particularly complicated tables --
		 (This will draw more lines: busier, but clearer.)

		 Use class="long" on table cells with paragraph-like contents
		 (This will adjust text alignment accordingly.)
		 Alternately use class="longlastcol" on tables, to have the last column assume "long".
	*/

	table {
		word-wrap: normal;
		overflow-wrap: normal;
		hyphens: manual;
	}

	table.data,
	table.index {
		margin: 1em auto;
		border-collapse: collapse;
		border: hidden;
		width: 100%;
	}
	table.data caption,
	table.index caption {
		max-width: 50em;
		margin: 0 auto 1em;
	}

	table.data td,  table.data th,
	table.index td, table.index th {
		padding: 0.5em 1em;
		border-width: 1px;
		border-color: silver;
		border-top-style: solid;
	}

	table.data thead td:empty {
		padding: 0;
		border: 0;
	}

	table.data  thead,
	table.index thead,
	table.data  tbody,
	table.index tbody {
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 <body class="h-entry">
  <div class="head">
   <p data-fill-with="logo"></p>
   <h1 class="p-name no-ref" id="title">P0323R9<br>std::expected</h1>
   <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Published Proposal, <time class="dt-updated" datetime="1970-01-01">1970-01-01</time></span></h2>
   <div data-fill-with="spec-metadata">
    <dl>
     <dt>This version:
     <dd><a class="u-url" href="https://wg21.link/P0323R9">https://wg21.link/P0323R9</a>
     <dt>Authors:
     <dd>
      <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:vicente.botet@nokia.com">Vicente Botet</a> (<span class="p-org org">Nokia</span>)
     <dd>
      <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:jfbastien@apple.com">JF Bastien</a> (<span class="p-org org">Apple</span>)
     <dt>Audience:
     <dd>LWG
     <dt>Project:
     <dd>ISO/IEC JTC1/SC22/WG21 14882: Programming Language — C++
     <dt>Source:
     <dd><a href="https://github.com/jfbastien/papers/blob/master/source/P0323R9.bs">github.com/jfbastien/papers/blob/master/source/P0323R9.bs</a>
    </dl>
   </div>
   <div data-fill-with="warning"></div>
   <hr title="Separator for header">
  </div>
  <div class="p-summary" data-fill-with="abstract">
   <h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
   <p>Utility class to represent expected object: wording and open questions.</p>
  </div>
  <nav data-fill-with="table-of-contents" id="toc">
   <h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
   <ol class="toc" role="directory">
    <li>
     <a href="#word"><span class="secno">1</span> <span class="content">Wording</span></a>
     <ol class="toc">
      <li><a href="#expected"><span class="secno">1.1</span> <span class="content">�.� Expected objects [<em>expected</em>]</span></a>
      <li><a href="#expected.general"><span class="secno">1.2</span> <span class="content">�.�.1 In general [<em>expected.general</em>]</span></a>
      <li><a href="#expected.synop"><span class="secno">1.3</span> <span class="content">�.�.2 Header <code class="highlight"><c- o>&lt;</c-><c- n>experimental</c-><c- o>/</c-><c- n>expected</c-><c- o>></c-></code> synopsis [<em>expected.synop</em>]</span></a>
      <li><a href="#expected.defs"><span class="secno">1.4</span> <span class="content">�.�.3 Definitions [<em>expected.defs</em>]</span></a>
      <li><a href="#expected.expected"><span class="secno">1.5</span> <span class="content">�.�.4 Class template expected [<em>expected.expected</em>]</span></a>
      <li><a href="#expected.object.ctor"><span class="secno">1.6</span> <span class="content">�.�.4.1 Constructors [<em>expected.object.ctor</em>]</span></a>
      <li><a href="#expected.object.dtor"><span class="secno">1.7</span> <span class="content">�.�.4.2 Destructor [<em>expected.object.dtor</em>]</span></a>
      <li><a href="#expected.object.assign"><span class="secno">1.8</span> <span class="content">�.�.4.3 Assignment [<em>expected.object.assign</em>]</span></a>
      <li><a href="#expected.object.swap"><span class="secno">1.9</span> <span class="content">�.�.4.4 Swap [<em>expected.object.swap</em>]</span></a>
      <li><a href="#expected.object.observe"><span class="secno">1.10</span> <span class="content">�.�.4.5 Observers [<em>expected.object.observe</em>]</span></a>
      <li><a href="#expected.equality_op"><span class="secno">1.11</span> <span class="content">�.�.4.6 Expected Equality operators [<em>expected.equality_op</em>]</span></a>
      <li><a href="#expected.comparison_T"><span class="secno">1.12</span> <span class="content">�.�.4.7 Comparison with <code class="highlight"><c- n>T</c-></code> [<em>expected.comparison_T</em>]</span></a>
      <li><a href="#expected.comparison_unexpected_E"><span class="secno">1.13</span> <span class="content">�.�.4.8 Comparison with <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> [<em>expected.comparison_unexpected_E</em>]</span></a>
      <li><a href="#expected.specalg"><span class="secno">1.14</span> <span class="content">�.�.4.9 Specialized algorithms [<em>expected.specalg</em>]</span></a>
      <li><a href="#expected.unexpected"><span class="secno">1.15</span> <span class="content">�.�.5 Unexpected objects [<em>expected.unexpected</em>]</span></a>
      <li><a href="#expected.unexpected.general"><span class="secno">1.16</span> <span class="content">�.�.5.1 General [<em>expected.unexpected.general</em>]</span></a>
      <li>
       <a href="#expected.unexpected.object"><span class="secno">1.17</span> <span class="content">�.�.5.2 Class template <code class="highlight"><c- n>unexpected</c-></code> [<em>expected.unexpected.object</em>]</span></a>
       <ol class="toc">
        <li><a href="#expected.unexpected.ctor"><span class="secno">1.17.1</span> <span class="content">�.�.5.2.1 Constructors [<em>expected.unexpected.ctor</em>]</span></a>
        <li><a href="#expected.unexpected.assign"><span class="secno">1.17.2</span> <span class="content">�.�.5.2.2 Assignment [<em>expected.unexpected.assign</em>]</span></a>
        <li><a href="#expected.unexpected.observe"><span class="secno">1.17.3</span> <span class="content">�.�.5.2.3 Observers [<em>expected.unexpected.observe</em>]</span></a>
        <li><a href="#expected.unexpected.swap"><span class="secno">1.17.4</span> <span class="content">�.�.5.2.4 Swap [<em>expected.unexpected.ctor</em>]</span></a>
       </ol>
      <li>
       <a href="#expected.unexpected.equality_op"><span class="secno">1.18</span> <span class="content">�.�.5.2.5 Equality operators [<em>expected.unexpected.equality_op</em>]</span></a>
       <ol class="toc">
        <li><a href="#expected.unexpected.specalg"><span class="secno">1.18.1</span> <span class="content">�.�.5.2.5 Specialized algorithms [<em>expected.unexpected.specalg</em>]</span></a>
       </ol>
      <li><a href="#expected.bad_expected_access"><span class="secno">1.19</span> <span class="content">�.�.6 Template Class <code class="highlight"><c- n>bad_expected_access</c-></code> [<em>expected.bad_expected_access</em>]</span></a>
      <li><a href="#expected.bad_expected_access_base"><span class="secno">1.20</span> <span class="content">�.�.7 Class <code class="highlight"><c- n>bad_expected_access</c-><c- o>&lt;</c-><c- b>void</c-><c- o>></c-></code> [<em>expected.bad_expected_access_base</em>]</span></a>
      <li><a href="#expected.unexpect"><span class="secno">1.21</span> <span class="content">�.�.8 <code class="highlight"><c- n>unexpect</c-></code> tag [<em>expected.unexpect</em>]</span></a>
     </ol>
    <li>
     <a href="#qq"><span class="secno">2</span> <span class="content">Open Questions</span></a>
     <ol class="toc">
      <li><a href="#ergo"><span class="secno">2.1</span> <span class="content">Ergonomics</span></a>
      <li><a href="#dis"><span class="secno">2.2</span> <span class="content">Disappointment</span></a>
      <li><a href="#stl"><span class="secno">2.3</span> <span class="content">STL Usage</span></a>
     </ol>
    <li>
     <a href="#references"><span class="secno"></span> <span class="content">References</span></a>
     <ol class="toc">
      <li><a href="#informative"><span class="secno"></span> <span class="content">Informative References</span></a>
     </ol>
    <li><a href="#issues-index"><span class="secno"></span> <span class="content">Issues Index</span></a>
   </ol>
  </nav>
  <main>
   <p>This paper is an update to <span>[P0323r8]</span>, with significant wording fixes provided
by the most wonderful Jonathan Wakely.</p>
   <p>Revision 7 was published a year prior to revision 8. No official LWG reviews
have occurred between revision 7 and 9. As you read this paper, it has been:</p>
   <ul>
    <li data-md>
     <p><span id="N4015"></span> since <a data-link-type="biblio" href="#biblio-n4015">[N4015]</a> was initially published.</p>
    <li data-md>
     <p><span id="firstLEWGReview"></span> since the first LEWG review.</p>
    <li data-md>
     <p><span id="forwarded"></span> since LEWG forwarded the paper to LWG for inclusion in the Library Fundamentals TS v3.</p>
   </ul>
   <p>Now that C++20 is winding down, the authors hope that LWG will be able to
finalize its wording review, and move the paper to the Library Fundamentals TS
v3. This will help the Committee obtain feedback on a feature which should be
able to make it to C++23.</p>
<script>
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  let res = "";
  if (y != 0) res +=       y + " year"  + (y > 1 ? "s" : "");
  if (m != 0) res += " " + m + " month" + (m > 1 ? "s" : "");
  return res;
};
const N4015 = new Date("2014-05-26");
const firstLEWGReview = new Date("2014-07-09T17:29:10");
const forwarded = new Date("2017-11-11T16:07:24");

document.getElementById('N4015').innerHTML = timeSince(N4015);
document.getElementById('firstLEWGReview').innerHTML = timeSince(firstLEWGReview);
document.getElementById('forwarded').innerHTML = timeSince(forwarded);
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   <p>Revision 7 of this paper revised <a data-link-type="biblio" href="#biblio-p0323r6">[P0323r6]</a> and <a data-link-type="biblio" href="#biblio-p0323r5">[P0323r5]</a> with feedback
received from LWG. <a data-link-type="biblio" href="#biblio-p0323r4">[P0323r4]</a> contains motivation, design rationale,
implementability information, sample usage, history, alternative designs and
related types. Revision 5 onwards only contain wording and open questions
because their purpose is twofold:</p>
   <ul>
    <li data-md>
     <p>Present appropriate wording for inclusion in the Library Fundamentals TS v3.</p>
    <li data-md>
     <p>List open questions which the TS should aim to answer.</p>
   </ul>
   <h2 class="heading settled" data-level="1" id="word"><span class="secno">1. </span><span class="content">Wording</span><a class="self-link" href="#word"></a></h2>
   <p>Below, substitute the <code class="highlight">�</code> character with a number or name the editor finds
appropriate for the sub-section.</p>
   <h3 class="heading settled" data-level="1.1" id="expected"><span class="secno">1.1. </span><span class="content">�.� Expected objects [<em>expected</em>]</span><a class="self-link" href="#expected"></a></h3>
   <h3 class="heading settled" data-level="1.2" id="expected.general"><span class="secno">1.2. </span><span class="content">�.�.1 In general [<em>expected.general</em>]</span><a class="self-link" href="#expected.general"></a></h3>
   <p>This subclause describes class template <code class="highlight"><c- n>expected</c-></code> that represents expected
objects. An <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> object holds an object of type <code class="highlight"><c- n>T</c-></code> or an object of
type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> and manages the lifetime of the contained objects.</p>
   <h3 class="heading settled" data-level="1.3" id="expected.synop"><span class="secno">1.3. </span><span class="content">�.�.2 Header <code class="highlight"><c- o>&lt;</c-><c- n>experimental</c-><c- o>/</c-><c- n>expected</c-><c- o>></c-></code> synopsis [<em>expected.synop</em>]</span><a class="self-link" href="#expected.synop"></a></h3>
<pre class="language-c++ highlight"><c- n>namespace</c-> <c- n>std</c-> <c- p>{</c->
<c- n>namespace</c-> <c- n>experimental</c-> <c- p>{</c->
<c- kr>inline</c-> <c- n>namespace</c-> <c- n>fundamentals_v3</c-> <c- p>{</c->
    <c- c1>// �.�.4, class template expected</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T</c-><c- p>,</c-> <c- n>class</c-> <c- n>E</c-><c- o>></c->
        <c- n>class</c-> <c- n>expected</c-><c- p>;</c->

    <c- c1>// �.�.5, class template unexpected</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>E</c-><c- o>></c->
        <c- n>class</c-> <c- n>unexpected</c-><c- p>;</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>E</c-><c- o>></c->
      <c- n>unexpected</c-><c- p>(</c-><c- n>E</c-><c- p>)</c-> <c- o>-></c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>;</c->

    <c- c1>// �.�.6, class bad_expected_access</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>E</c-><c- o>></c->
       <c- n>class</c-> <c- n>bad_expected_access</c-><c- p>;</c->

    <c- c1>// �.�.7, Specialization for void</c->
    <c- n>template</c-><c- o>&lt;></c->
       <c- n>class</c-> <c- n>bad_expected_access</c-><c- o>&lt;</c-><c- b>void</c-><c- o>></c-><c- p>;</c->

    <c- c1>// �.�.8, unexpect tag</c->
    <c- k>struct</c-> <c- n>unexpect_t</c-> <c- p>{</c->
       <c- n>explicit</c-> <c- n>unexpect_t</c-><c- p>()</c-> <c- o>=</c-> <c- k>default</c-><c- p>;</c->
    <c- p>};</c->
    <c- kr>inline</c-> <c- n>constexpr</c-> <c- n>unexpect_t</c-> <c- n>unexpect</c-><c- p>{};</c->

<c- p>}}}</c->
</pre>
   <h3 class="heading settled" data-level="1.4" id="expected.defs"><span class="secno">1.4. </span><span class="content">�.�.3 Definitions [<em>expected.defs</em>]</span><a class="self-link" href="#expected.defs"></a></h3>
   <h3 class="heading settled" data-level="1.5" id="expected.expected"><span class="secno">1.5. </span><span class="content">�.�.4 Class template expected [<em>expected.expected</em>]</span><a class="self-link" href="#expected.expected"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T</c-><c- p>,</c-> <c- n>class</c-> <c- n>E</c-><c- o>></c->
<c- n>class</c-> <c- n>expected</c-> <c- p>{</c->
<c- nl>public</c-><c- p>:</c->
    <c- n>using</c-> <c- n>value_type</c-> <c- o>=</c-> <c- n>T</c-><c- p>;</c->
    <c- n>using</c-> <c- n>error_type</c-> <c- o>=</c-> <c- n>E</c-><c- p>;</c->
    <c- n>using</c-> <c- n>unexpected_type</c-> <c- o>=</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>;</c->

    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- o>></c->
    <c- n>using</c-> <c- n>rebind</c-> <c- o>=</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>error_type</c-><c- o>></c-><c- p>;</c->

    <c- c1>// �.�.4.1, constructors</c->
    <c- n>constexpr</c-> <c- nf>expected</c-><c- p>();</c->
    <c- n>constexpr</c-> <c- nf>expected</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&amp;</c-><c- p>);</c->
    <c- n>constexpr</c-> <c- nf>expected</c-><c- p>(</c-><c- n>expected</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-> <c- n>G</c-><c- o>></c->
        <c- n>explicit</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>)</c-> <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-> <c- n>G</c-><c- o>></c->
        <c- n>explicit</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>)</c-> <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>);</c->

    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-> <c- o>=</c-> <c- n>T</c-><c- o>></c->
        <c- n>explicit</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>)</c-> <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-> <c- n>v</c-><c- p>);</c->

    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>G</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>G</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>);</c->

    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>expected</c-><c- p>(</c-><c- n>in_place_t</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>expected</c-><c- p>(</c-><c- n>in_place_t</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>expected</c-><c- p>(</c-><c- n>unexpect_t</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>expected</c-><c- p>(</c-><c- n>unexpect_t</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->


    <c- c1>// �.�.4.2, destructor</c->
    <c- o>~</c-><c- n>expected</c-><c- p>();</c->

    <c- c1>// �.�.4.3, assignment</c->
    <c- n>expected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&amp;</c-><c- p>);</c->
    <c- n>expected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- n>expected</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-> <c- o>=</c-> <c- n>T</c-><c- o>></c-> <c- n>expected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-><c- p>);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>G</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
        <c- n>expected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>G</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
        <c- n>expected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>);</c->

    <c- c1>// �.�.4.4, modifiers</c->

    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
        <c- n>T</c-><c- o>&amp;</c-> <c- n>emplace</c-><c- p>(</c-><c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
        <c- n>T</c-><c- o>&amp;</c-> <c- n>emplace</c-><c- p>(</c-><c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->

    <c- c1>// �.�.4.5, swap</c->
    <c- b>void</c-> <c- nf>swap</c-><c- p>(</c-><c- n>expected</c-><c- o>&amp;</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->

    <c- c1>// �.�.4.6, observers</c->
    <c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>*</c-> <c- n>operator</c-><c- o>-></c-><c- p>()</c-> <c- k>const</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>T</c-><c- o>*</c-> <c- n>operator</c-><c- o>-></c-><c- p>();</c->
    <c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>*</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>*</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>operator</c-><c- o>*</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>operator</c-><c- o>*</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>operator</c-> <c- nf>bool</c-><c- p>()</c-> <c- k>const</c-> <c- n>noexcept</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- b>bool</c-> <c- nf>has_value</c-><c- p>()</c-> <c- k>const</c-> <c- n>noexcept</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- k>const</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- k>const</c-> <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>T</c-> <c- n>value_or</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>T</c-> <c- n>value_or</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- o>&amp;&amp;</c-><c- p>;</c->

    <c- c1>// �.�.4.7, Expected equality operators</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
        <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T2</c-><c- p>,</c-> <c- n>E2</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
        <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T2</c-><c- p>,</c-> <c- n>E2</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>);</c->

    <c- c1>// �.�.4.8, Comparison with T</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- o>></c->
        <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-><c- p>);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- o>></c->
        <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- o>></c->
        <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-><c- p>);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- o>></c->
        <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>);</c->

    <c- c1>// �.�.4.9, Comparison with unexpected&lt;E></c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
        <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
        <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
        <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
        <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>);</c->

    <c- c1>// �.�.4.10, Specialized algorithms</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- o>></c->
        <c- n>friend</c-> <c- b>void</c-> <c- n>swap</c-><c- p>(</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->

<c- nl>private</c-><c- p>:</c->
    <c- b>bool</c-> <c- n>has_val</c-><c- p>;</c-> <c- c1>// exposition only</c->
    <c- k>union</c->
    <c- p>{</c->
        <c- n>value_type</c-> <c- n>val</c-><c- p>;</c-> <c- c1>// exposition only</c->
        <c- n>unexpected_type</c-> <c- n>unex</c-><c- p>;</c-> <c- c1>// exposition only</c->
    <c- p>};</c->
<c- p>};</c->
</pre>
   <p>Any object of <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> either contains a value of type <code class="highlight"><c- n>T</c-></code> or a value of
type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> within its own storage. Implementations are not permitted
to use additional storage, such as dynamic memory, to allocate the object of
type <code class="highlight"><c- n>T</c-></code> or the object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>. These objects are allocated
in a region of the <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> storage suitably aligned for the types <code class="highlight"><c- n>T</c-></code> and <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>. Members <code class="highlight"><c- n>has_val</c-></code>, <code class="highlight"><c- n>val</c-></code> and <code class="highlight"><c- n>unex</c-></code> are provided for
exposition only. <code class="highlight"><c- n>has_val</c-></code> indicates whether the <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> object
contains an object of type <code class="highlight"><c- n>T</c-></code>.</p>
   <p>A program that instantiates the definition of template <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> for a
reference type, a function type, or for possibly cv-qualified types <code class="highlight"><c- n>in_place_t</c-></code>, <code class="highlight"><c- n>unexpect_t</c-></code> or <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> for the <code class="highlight"><c- n>T</c-></code> parameter is
ill-formed. A program that instantiates the definition of template <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with the <code class="highlight"><c- n>E</c-></code> parameter that is not a valid template parameter
for <code class="highlight"><c- n>unexpected</c-></code> is ill-formed.</p>
   <p>When <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code>, it shall meet the requirements of <code class="highlight"><c- n>Cpp17Destructible</c-></code> (Table 27).</p>
   <p><code class="highlight"><c- n>E</c-></code> shall meet the requirements of <code class="highlight"><c- n>Cpp17Destructible</c-></code> (Table 27).</p>
   <h3 class="heading settled" data-level="1.6" id="expected.object.ctor"><span class="secno">1.6. </span><span class="content">�.�.4.1 Constructors [<em>expected.object.ctor</em>]</span><a class="self-link" href="#expected.object.ctor"></a></h3>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- nf>expected</c-><c- p>();</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>is_default_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> or <code class="highlight"><c- n>T</c-></code> is <em>cv</em> <code class="highlight"><c- b>void</c-></code>.</p>
   <p><em>Effects</em>: Value-initializes <code class="highlight"><c- n>val</c-></code> if <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>T</c-></code>.</p>
   <p><em>Remarks</em>: If value-initialization of <code class="highlight"><c- n>T</c-></code> is a constant subexpression or <code class="highlight"><c- n>T</c-></code> is <em>cv</em> <code class="highlight"><c- b>void</c-></code> this constructor is constexpr.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- nf>expected</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&amp;</c-> <c- n>rhs</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code> and <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code>, initializes <code class="highlight"><c- n>val</c-></code> as if
direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with the expression <code class="highlight"><c- o>*</c-><c- n>rhs</c-></code>.</p>
   <p>Otherwise, initializes <code class="highlight"><c- n>unex</c-></code> as if direct-non-list-initializing an object
of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with the expression <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-> <c- o>==</c-> <c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>T</c-></code> or <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>: This constructor is defined as deleted unless:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>is_copy_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> or <code class="highlight"><c- n>T</c-></code> is <em>cv</em> <code class="highlight"><c- b>void</c-></code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_copy_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   </ul>
   <p>This constructor is a constexpr constructor if:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>is_trivially_copy_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> or <code class="highlight"><c- n>T</c-></code> is <em>cv</em> <code class="highlight"><c- b>void</c-></code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_trivially_copy_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   </ul>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- nf>expected</c-><c- p>(</c-><c- n>expected</c-><c- o>&amp;&amp;</c-> <c- n>rhs</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   </ul>
   <p><em>Effects</em>: If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code> and <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code>, initializes <code class="highlight"><c- n>val</c-></code> as if
direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with the expression <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- o>*</c-><c- n>rhs</c-><c- p>)</c-></code>.</p>
   <p>Otherwise, initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of
type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with the expression <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>()))</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code> is unchanged, <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-> <c- o>==</c-> <c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>T</c-></code> or <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>: The expression inside <code class="highlight"><c- k>noexcept</c-></code> is equivalent to:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> or <code class="highlight"><c- n>T</c-></code>is <em>cv</em> <code class="highlight"><c- b>void</c-></code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   </ul>
   <p><em>Remarks</em>: This constructor is a constexpr constructor if:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>is_trivially_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> or <code class="highlight"><c- n>T</c-></code> is <em>cv</em> <code class="highlight"><c- b>void</c-></code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_trivially_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   </ul>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-> <c- n>G</c-><c- o>></c->
    <c- n>explicit</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>)</c-> <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-> <c- n>rhs</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>T</c-></code> and <code class="highlight"><c- n>U</c-></code> are <em>cv</em> <code class="highlight"><c- b>void</c-></code> or:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- k>const</c-> <c- n>U</c-><c- o>&amp;></c-></code> is <code class="highlight">true</code> ; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- k>const</c-> <c- n>G</c-><c- o>&amp;></c-></code> is <code class="highlight">true</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>>></c-></code> is <code class="highlight">false</code>.</p>
   </ul>
   <p><em>Effects</em>: If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code> and <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code>, initializes <code class="highlight"><c- n>val</c-></code> as if
direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with the expression <code class="highlight"><c- o>*</c-><c- n>rhs</c-></code>.</p>
   <p>Otherwise, initializes <code class="highlight"><c- n>unex</c-></code> as if direct-non-list-initializing an object
of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with the expression <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-> <c- o>==</c-> <c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>T</c-></code> or <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>:
The expression inside <code class="highlight"><c- k>explicit</c-></code> is <code class="highlight">true</code> if and only if:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>T</c-></code> and <code class="highlight"><c- n>U</c-></code> are not <em>cv</em> <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>U</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code> or</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>G</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>.</p>
   </ul>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-> <c- n>G</c-><c- o>></c->
    <c- n>explicit</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>)</c-> <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-> <c- n>rhs</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>T</c-></code> and <code class="highlight"><c- n>U</c-></code> are <em>cv</em> <code class="highlight"><c- b>void</c-></code> or:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>U</c-><c- o>&amp;&amp;></c-></code> is <code class="highlight">true</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>G</c-><c- o>&amp;&amp;></c-></code> is <code class="highlight">true</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>>></c-></code> is <code class="highlight">false</code>.</p>
   </ul>
   <p><em>Effects</em>: If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code> initializes <code class="highlight"><c- n>val</c-></code> as if
direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with the expression <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- o>*</c-><c- n>rhs</c-><c- p>)</c-></code> or nothing if <code class="highlight"><c- n>T</c-></code> is <em>cv</em> <code class="highlight"><c- b>void</c-></code>.</p>
   <p>Otherwise, initializes <code class="highlight"><c- n>unex</c-></code> as if direct-non-list-initializing an object
of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with the expression <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>()))</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code> is unchanged, <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-> <c- o>==</c-> <c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by operations specified in the effect clause.</p>
   <p><em>Remarks</em>: The expression inside <code class="highlight"><c- k>explicit</c-></code> is <code class="highlight">true</code> if and only if</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>T</c-></code> and <code class="highlight"><c- n>U</c-></code> are not <em>cv</em> <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>U</c-><c- o>&amp;&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code> or</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>G</c-><c- o>&amp;&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>.</p>
   </ul>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-> <c- o>=</c-> <c- n>T</c-><c- o>></c->
    <c- n>explicit</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>)</c-> <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-> <c- n>v</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>U</c-><c- o>&amp;&amp;></c-></code> is <code class="highlight">true</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_same_v</c-><c- o>&lt;</c-><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>,</c-> <c- n>in_place_t</c-><c- o>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_same_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-><c- p>,</c-> <c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_same_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>></c-></code> is <code class="highlight">false</code>.</p>
   </ul>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an
object of type <code class="highlight"><c- n>T</c-></code> with the expression <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>(</c-><c- n>v</c-><c- p>)</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>T</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>T</c-></code>'s selected constructor is a constant subexpression, this
constructor is a constexpr constructor.</p>
   <p><em>Remarks</em>: The expression inside <code class="highlight"><c- k>explicit</c-></code> is equivalent to <code class="highlight"><c- o>!</c-><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>U</c-><c- o>&amp;&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>G</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
    <c- n>explicit</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>)</c-> <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>>&amp;</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- k>const</c-> <c- n>G</c-><c- o>&amp;></c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>unex</c-></code> as if direct-non-list-initializing
an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with the expression <code class="highlight"><c- n>e</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">false</code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>'s selected constructor is a constant
subexpression, this constructor shall be a constexpr constructor.
The expression inside <code class="highlight"><c- k>explicit</c-></code> is equivalent to <code class="highlight"><c- o>!</c-><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>G</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>G</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
    <c- n>explicit</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>)</c-> <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>>&amp;&amp;</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>G</c-><c- o>&amp;&amp;></c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>unex</c-></code> as if direct-non-list-initializing
an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with the expression <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>e</c-><c- p>)</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">false</code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>'s selected constructor is a constant
subexpression, this constructor is a constexpr constructor. The expression
inside <code class="highlight"><c- k>noexcept</c-></code> is equivalent to: <code class="highlight"><c- n>is_nothrow_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>G</c-><c- o>&amp;&amp;></c-></code> is <code class="highlight">true</code>.
The expression inside <code class="highlight"><c- k>explicit</c-></code> is equivalent to <code class="highlight"><c- o>!</c-><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>G</c-><c- o>&amp;&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>expected</c-><c- p>(</c-><c- n>in_place_t</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-> <c- n>args</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>T</c-></code> is <em>cv</em> <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- k>sizeof</c-><c- p>...(</c-><c- n>Args</c-><c- p>)</c-> <c- o>==</c-> <c- mi>0</c-></code>; or</p>
    <li data-md>
     <p><code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Args</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   </ul>
   <p><em>Effects</em>: If <code class="highlight"><c- n>T</c-></code> is <em>cv</em> <code class="highlight"><c- b>void</c-></code>, no effects. Otherwise, initializes <code class="highlight"><c- n>val</c-></code> as if
direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with the arguments <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>T</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>T</c-></code>'s constructor selected for the initialization is a constant subexpression,
this constructor is a constexpr constructor.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>expected</c-><c- p>(</c-><c- n>in_place_t</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-> <c- n>il</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-> <c- n>args</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>Args</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an
object of type <code class="highlight"><c- n>T</c-></code> with the arguments <code class="highlight"><c- n>il</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>T</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>T</c-></code>'s constructor selected for the initialization is a constant subexpression,
this constructor is a constexpr constructor.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>expected</c-><c- p>(</c-><c- n>unexpect_t</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-> <c- n>args</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>Args</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>unex</c-></code> as if direct-non-list-initializing
an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>with the arguments <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">false</code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>'s constructor selected for the initialization is a
constant subexpression, this constructor is a constexpr constructor.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>expected</c-><c- p>(</c-><c- n>unexpect_t</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-> <c- n>il</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-> <c- n>args</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>Args</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>unex</c-></code> as if direct-non-list-initializing
an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with the arguments <code class="highlight"><c- n>il</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">false</code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>'s constructor selected for the initialization is a
constant subexpression, this constructor is a constexpr constructor.</p>
   <h3 class="heading settled" data-level="1.7" id="expected.object.dtor"><span class="secno">1.7. </span><span class="content">�.�.4.2 Destructor [<em>expected.object.dtor</em>]</span><a class="self-link" href="#expected.object.dtor"></a></h3>
<pre class="language-c++ highlight"><c- o>~</c-><c- n>expected</c-><c- p>();</c->
</pre>
   <p><em>Effects</em>: If <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_trivially_destructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code> and <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>, calls <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code>. If <code class="highlight"><c- n>is_trivially_destructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code> and <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>, calls <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>.</p>
   <p><em>Remarks</em>: If either <code class="highlight"><c- n>T</c-></code> is <em>cv</em> <code class="highlight"><c- b>void</c-></code> or <code class="highlight"><c- n>is_trivially_destructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>, and <code class="highlight"><c- n>is_trivially_destructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>, then this destructor
is a trivial destructor.</p>
   <h3 class="heading settled" data-level="1.8" id="expected.object.assign"><span class="secno">1.8. </span><span class="content">�.�.4.3 Assignment [<em>expected.object.assign</em>]</span><a class="self-link" href="#expected.object.assign"></a></h3>
<pre class="language-c++ highlight"><c- n>expected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&amp;</c-> <c- n>rhs</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: See Table <em>editor-please-pick-a-number-0</em></p>
   <table>
    <caption>Table <em>editor-please-pick-a-number-0</em> — <code class="highlight"><c- k>operator</c-><c- o>=</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&amp;</c-><c- p>)</c-></code> effects</caption>
    <tbody>
     <tr>
      <td>
      <td><code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>
      <td><code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>
     <tr>
      <td><code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>
      <td>assigns <code class="highlight"><c- o>*</c-><c- n>rhs</c-></code> to <code class="highlight"><c- n>val</c-></code> if <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code>
      <td>
       <ul>
        <li data-md>
         <p>if <code class="highlight"><c- n>T</c-></code> is <em>cv</em> <code class="highlight"><c- b>void</c-></code> destroys <code class="highlight"><c- n>unex</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code> and set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>,</p>
        <li data-md>
         <p>otherwise if <code class="highlight"><c- n>is_nothrow_copy_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
         <ul>
          <li data-md>
           <p>destroys <code class="highlight"><c- n>unex</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code></p>
          <li data-md>
           <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- o>*</c-><c- n>rhs</c-></code>;</p>
         </ul>
        <li data-md>
         <p>otherwise if <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
         <ul>
          <li data-md>
           <p>constructs a <code class="highlight"><c- n>T</c-> <c- n>tmp</c-></code> from <code class="highlight"><c- o>*</c-><c- n>rhs</c-></code> (this can throw),</p>
          <li data-md>
           <p>destroys <code class="highlight"><c- n>unex</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code></p>
          <li data-md>
           <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>tmp</c-><c- p>)</c-></code>;</p>
         </ul>
        <li data-md>
         <p>otherwise</p>
         <ul>
          <li data-md>
           <p>constructs an <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-> <c- n>tmp</c-></code> from <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- k>this</c-><c- o>-></c-><c- n>error</c-><c- p>())</c-></code> (which can throw),</p>
          <li data-md>
           <p>destroys <code class="highlight"><c- n>unex</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
          <li data-md>
           <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- o>*</c-><c- n>rhs</c-></code>. Either,</p>
          <li data-md>
           <p>the constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>, or</p>
          <li data-md>
           <p>the constructor did throw, so move-construct the <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>), and rethrow the exception.</p>
         </ul>
       </ul>
     <tr>
      <td><code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>
      <td>
       <ul>
        <li data-md>
         <p>if <code class="highlight"><c- n>T</c-></code> is <em>cv</em> <code class="highlight"><c- b>void</c-></code></p>
         <ul>
          <li data-md>
           <p>initializes <code class="highlight"><c- n>unex</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code>. Either</p>
          <li data-md>
           <p>the constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">false</code>, or</p>
          <li data-md>
           <p>the constructor did throw, and nothing was changed.</p>
         </ul>
        <li data-md>
         <p>otherwise if <code class="highlight"><c- n>is_nothrow_copy_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
         <ul>
          <li data-md>
           <p>destroys <code class="highlight"><c- n>val</c-></code> by calling <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code>,</p>
          <li data-md>
           <p>initializes <code class="highlight"><c- n>unex</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code> and set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">false</code>.</p>
         </ul>
        <li data-md>
         <p>otherwise if <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
         <ul>
          <li data-md>
           <p>constructs an <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-> <c- n>tmp</c-></code> from <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code> (this can throw),</p>
          <li data-md>
           <p>destroys <code class="highlight"><c- n>val</c-></code> by calling <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code>,</p>
          <li data-md>
           <p>initializes <code class="highlight"><c- n>unex</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>tmp</c-><c- p>)</c-></code> and set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">false</code>.</p>
         </ul>
        <li data-md>
         <p>otherwise</p>
         <ul>
          <li data-md>
           <p>constructs a <code class="highlight"><c- n>T</c-> <c- n>tmp</c-></code> from <code class="highlight"><c- o>*</c-><c- k>this</c-></code> (this can throw),</p>
          <li data-md>
           <p>destroys <code class="highlight"><c- n>val</c-></code> by calling <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code>,</p>
          <li data-md>
           <p>initializes <code class="highlight"><c- n>unex</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code>. Either,</p>
          <li data-md>
           <p>the last constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">false</code>, or</p>
          <li data-md>
           <p>the last constructor did throw, so move-construct the <code class="highlight"><c- n>T</c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>), and rethrow the exception.</p>
         </ul>
       </ul>
      <td>assigns <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code> to <code class="highlight"><c- n>unex</c-></code>
   </table>
   <p><em>Returns</em>: <code class="highlight"><c- o>*</c-><c- k>this</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-> <c- o>==</c-> <c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the operations specified in the effect clause.</p>
   <p><em>Remarks</em>: If any exception is thrown, <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> and <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code> remain unchanged.</p>
   <p>If an exception is thrown during the call to <code class="highlight"><c- n>T</c-></code>'s or <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>'s copy
constructor, no effect. If an exception is thrown during the call to <code class="highlight"><c- n>T</c-></code>'s or <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>'s copy assignment, the state of its contained value is as defined
by the exception safety guarantee of <code class="highlight"><c- n>T</c-></code>'s or <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>'s copy assignment.</p>
   <p>This operator is defined as deleted unless:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>T</c-></code> is <em>cv</em> <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_copy_assignable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_copy_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>; or</p>
    <li data-md>
     <p><code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_copy_assignable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_copy_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_copy_assignable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_copy_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> and
(<code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> or <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>).</p>
   </ul>
<pre class="language-c++ highlight"><c- n>expected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- n>expected</c-><c- o>&amp;&amp;</c-> <c- n>rhs</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: See Table <em>editor-please-pick-a-number-1</em></p>
   <table>
    <caption>Table <em>editor-please-pick-a-number-1</em> — <code class="highlight"><c- k>operator</c-><c- o>=</c-><c- p>(</c-><c- n>expected</c-><c- o>&amp;&amp;</c-><c- p>)</c-></code> effects</caption>
    <tbody>
     <tr>
      <td>
      <td><code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>
      <td><code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>
     <tr>
      <td><code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>
      <td>move assign <code class="highlight"><c- o>*</c-><c- n>rhs</c-></code> to <code class="highlight"><c- n>val</c-></code> if <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code>
      <td>
       <ul>
        <li data-md>
         <p>if <code class="highlight"><c- n>T</c-></code> is <em>cv</em> <code class="highlight"><c- b>void</c-></code> destroys <code class="highlight"><c- n>unex</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code></p>
        <li data-md>
         <p>otherwise if <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
         <ul>
          <li data-md>
           <p>destroys <code class="highlight"><c- n>unex</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
          <li data-md>
           <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- o>*</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>;</p>
         </ul>
        <li data-md>
         <p>otherwise</p>
         <ul>
          <li data-md>
           <p>move constructs an <code class="highlight"><c- n>unexpected_type</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-> <c- n>tmp</c-></code> from <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- k>this</c-><c- o>-></c-><c- n>error</c-><c- p>())</c-></code> (which can’t throw as <code class="highlight"><c- n>E</c-></code> is nothrow-move-constructible),</p>
          <li data-md>
           <p>destroys <code class="highlight"><c- n>unex</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
          <li data-md>
           <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- o>*</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>. Either,</p>
          <li data-md>
           <p>The constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>, or</p>
          <li data-md>
           <p>The constructor did throw, so move-construct the <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>E</c-></code> is nothrow-move-constructible), and rethrow the exception.</p>
         </ul>
       </ul>
     <tr>
      <td><code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>
      <td>
       <ul>
        <li data-md>
         <p>if <code class="highlight"><c- n>T</c-></code> is <em>cv</em> <code class="highlight"><c- b>void</c-></code></p>
         <ul>
          <li data-md>
           <p>initializes <code class="highlight"><c- n>unex</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>move</c-><c- p>(</c-><c- n>rhs</c-><c- p>).</c-><c- n>error</c-><c- p>())</c-></code>. Either</p>
          <li data-md>
           <p>the constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">false</code>, or</p>
          <li data-md>
           <p>the constructor did throw, and nothing was changed.</p>
         </ul>
        <li data-md>
         <p>otherwise if <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
         <ul>
          <li data-md>
           <p>destroys <code class="highlight"><c- n>val</c-></code> by calling <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code>,</p>
          <li data-md>
           <p>initializes <code class="highlight"><c- n>unex</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>()))</c-></code>;</p>
         </ul>
        <li data-md>
         <p>otherwise</p>
         <ul>
          <li data-md>
           <p>move constructs a <code class="highlight"><c- n>T</c-> <c- n>tmp</c-></code> from <code class="highlight"><c- o>*</c-><c- k>this</c-></code> (which can’t throw as <code class="highlight"><c- n>T</c-></code> is nothrow-move-constructible),</p>
          <li data-md>
           <p>destroys <code class="highlight"><c- n>val</c-></code> by calling <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code>,</p>
          <li data-md>
           <p>initializes <code class="highlight"><c- n>unex</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected_type</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>()))</c-></code>. Either,</p>
          <li data-md>
           <p>The constructor didn’t throw, so mark the expected as holding a <code class="highlight"><c- n>unexpected_type</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>, or</p>
          <li data-md>
           <p>The constructor did throw, so move-construct the <code class="highlight"><c- n>T</c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>T</c-></code> is nothrow-move-constructible), and rethrow the exception.</p>
         </ul>
       </ul>
      <td>move assign <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code> to <code class="highlight"><c- n>unex</c-></code>
   </table>
   <p><em>Returns</em>: <code class="highlight"><c- o>*</c-><c- k>this</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-> <c- o>==</c-> <c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Remarks</em>: The expression inside noexcept is equivalent to: <code class="highlight"><c- n>is_nothrow_move_assignable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <p>If any exception is thrown, <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> and <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code> remain
unchanged. If an exception is thrown during the call to <code class="highlight"><c- n>T</c-></code>'s copy constructor,
no effect. If an exception is thrown during the call to <code class="highlight"><c- n>T</c-></code>'s copy assignment,
the state of its contained value is as defined by the exception safety guarantee
of <code class="highlight"><c- n>T</c-></code>'s copy assignment. If an exception is thrown during the call to <code class="highlight"><c- n>E</c-></code>'s
copy assignment, the state of its contained <code class="highlight"><c- n>unex</c-></code> is as defined by
the exception safety guarantee of <code class="highlight"><c- n>E</c-></code>'s copy assignment.</p>
   <p>This operator is defined as deleted unless:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>T</c-></code> is <em>cv</em> <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_nothrow_move_assignable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>; or</p>
    <li data-md>
     <p><code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_move_assignable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_nothrow_move_assignable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   </ul>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-> <c- o>=</c-> <c- n>T</c-><c- o>></c->
    <c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-> <c- n>v</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>is_void_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_same_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>conjunction_v</c-><c- o>&lt;</c-><c- n>is_scalar</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>,</c-> <c- n>is_same</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>decay_t</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>U</c-><c- o>></c-></code> is <code class="highlight">true</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_assignable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>U</c-><c- o>></c-></code> is <code class="highlight">true</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   </ul>
   <p><em>Effects</em>: See Table <em>editor-please-pick-a-number-2</em></p>
   <table>
    <caption>Table <em>editor-please-pick-a-number-2</em> — <code class="highlight"><c- k>operator</c-><c- o>=</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-><c- p>)</c-></code> effects</caption>
    <tbody>
     <tr>
      <td><code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>
      <td><code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>
     <tr>
      <td>If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>, assigns <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>(</c-><c- n>v</c-><c- p>)</c-></code> to <code class="highlight"><c- n>val</c-></code>
      <td>
       <p>if <code class="highlight"><c- n>is_nothrow_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>U</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
       <ul>
        <li data-md>
         <p>destroys <code class="highlight"><c- n>unex</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
        <li data-md>
         <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>(</c-><c- n>v</c-><c- p>)</c-></code> and</p>
        <li data-md>
         <p>set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>;</p>
       </ul>
       <p>otherwise</p>
       <ul>
        <li data-md>
         <p>move constructs an <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-> <c- n>tmp</c-></code> from <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- k>this</c-><c- o>-></c-><c- n>error</c-><c- p>())</c-></code> (which can’t throw as <code class="highlight"><c- n>E</c-></code> is nothrow-move-constructible),</p>
        <li data-md>
         <p>destroys <code class="highlight"><c- n>unex</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
        <li data-md>
         <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>(</c-><c- n>v</c-><c- p>)</c-></code>. Either,</p>
         <ul>
          <li data-md>
           <p>the constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>, that is set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>, or</p>
          <li data-md>
           <p>the constructor did throw, so move construct the <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>E</c-></code> is nothrow-move-constructible), and re-throw the exception.</p>
         </ul>
       </ul>
   </table>
   <p><em>Returns</em>: <code class="highlight"><c- o>*</c-><c- k>this</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Remarks</em>: If any exception is thrown, <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> remains
 unchanged. If an exception is thrown during the call to <code class="highlight"><c- n>T</c-></code>'s constructor, no
 effect. If an exception is thrown during the call to <code class="highlight"><c- n>T</c-></code>'s copy assignment, the
 state of its contained value is as defined by the exception safety guarantee of <code class="highlight"><c- n>T</c-></code>'s copy assignment.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>G</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
    <c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>>&amp;</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>is_nothrow_copy_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_copy_assignable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Effects</em>: See Table <em>editor-please-pick-a-number-3</em></p>
   <table>
    <caption>Table <em>editor-please-pick-a-number-3</em> — <code class="highlight"><c- k>operator</c-><c- o>=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>>&amp;</c-><c- p>)</c-></code> effects</caption>
    <tbody>
     <tr>
      <td><code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>
      <td><code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>
     <tr>
      <td>assigns <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>e</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code> to <code class="highlight"><c- n>unex</c-></code>
      <td>
       <ul>
        <li data-md>
         <p>destroys <code class="highlight"><c- n>val</c-></code> by calling <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code> if <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code>,</p>
        <li data-md>
         <p>initializes <code class="highlight"><c- n>unex</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>e</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code> and set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">false</code>.</p>
       </ul>
   </table>
   <p><em>Returns</em>: <code class="highlight"><c- o>*</c-><c- k>this</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">false</code>.</p>
   <p><em>Remarks</em>: If any exception is thrown, <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> remains unchanged.</p>
<pre class="language-c++ highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>>&amp;&amp;</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: See Table <em>editor-please-pick-a-number-4</em></p>
   <table>
    <caption>Table <em>editor-please-pick-a-number-4</em> — <code class="highlight"><c- k>operator</c-><c- o>=</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>>&amp;&amp;</c-> <c- n>e</c-><c- p>)</c-></code> effects</caption>
    <tbody>
     <tr>
      <td><code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>
      <td><code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>
     <tr>
      <td>
       <ul>
        <li data-md>
         <p>destroys <code class="highlight"><c- n>val</c-></code> by calling <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code> if <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code>,</p>
        <li data-md>
         <p>initializes <code class="highlight"><c- n>unex</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>e</c-><c- p>.</c-><c- n>error</c-><c- p>()))</c-></code> and set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">false</code>.</p>
       </ul>
      <td>move assign <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>e</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code> to <code class="highlight"><c- n>unex</c-></code>
   </table>
   <p><em>Constraints</em>: <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_move_assignable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Returns</em>: <code class="highlight"><c- o>*</c-><c- k>this</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">false</code>.</p>
   <p><em>Remarks</em>: If any exception is thrown, <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> remains unchanged.</p>
<pre class="language-c++ highlight"><c- b>void</c-> <c- n>expected</c-><c- o>&lt;</c-><c- b>void</c-><c- p>,</c-> <c- n>E</c-><c- o>>::</c-><c- n>emplace</c-><c- p>();</c->
</pre>
   <p><em>Effects</em>:</p>
   <p>If <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code></p>
   <ul>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>unex</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
    <li data-md>
     <p>set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code></p>
   </ul>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Throws</em>: Nothing</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
    <c- n>T</c-><c- o>&amp;</c-> <c- n>emplace</c-><c- p>(</c-><c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-> <c- n>args</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_nothrow_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Args</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Effects</em>:</p>
   <p>If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>, assigns <code class="highlight"><c- n>val</c-></code> as if
constructing an object of type <code class="highlight"><c- n>T</c-></code> with the arguments <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code></p>
   <p>otherwise if <code class="highlight"><c- n>is_nothrow_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Args</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
   <ul>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>unex</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
    <li data-md>
     <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code> and</p>
    <li data-md>
     <p>set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>;</p>
   </ul>
   <p>otherwise if <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
   <ul>
    <li data-md>
     <p>constructs a <code class="highlight"><c- n>T</c-> <c- n>tmp</c-></code> from <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code> (which can throw),</p>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>unex</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
    <li data-md>
     <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>tmp</c-><c- p>)</c-></code> (which cannot throw) and</p>
    <li data-md>
     <p>set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>;</p>
   </ul>
   <p>otherwise</p>
   <ul>
    <li data-md>
     <p>move constructs an <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-> <c- n>tmp</c-></code> from <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- k>this</c-><c- o>-></c-><c- n>error</c-><c- p>())</c-></code> ,</p>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>unex</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
    <li data-md>
     <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code>. Either,</p>
     <ul>
      <li data-md>
       <p>the constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>, or</p>
      <li data-md>
       <p>the constructor did throw, so move-construct the <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>E</c-></code> is nothrow-move-constructible), and re-throw the exception.</p>
     </ul>
   </ul>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Returns:</em> A reference to the new contained value <code class="highlight"><c- n>val</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the operations specified in the effect clause.</p>
   <p><em>Remarks</em>: If an exception is thrown during the call to <code class="highlight"><c- n>T</c-></code>'s assignment, nothing
changes.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
    <c- n>T</c-><c- o>&amp;</c-> <c- n>emplace</c-><c- p>(</c-><c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-> <c- n>il</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-> <c- n>args</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_nothrow_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>Args</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Effects</em>:</p>
   <p>If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>, assigns <code class="highlight"><c- n>val</c-></code> as if
constructing an object of type <code class="highlight"><c- n>T</c-></code> with the arguments <code class="highlight"><c- n>il</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code></p>
   <p>otherwise if <code class="highlight"><c- n>is_nothrow_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>Args</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
   <ul>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>unex</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
    <li data-md>
     <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>il</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code> and</p>
    <li data-md>
     <p>set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>;</p>
   </ul>
   <p>otherwise if <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
   <ul>
    <li data-md>
     <p>constructs a <code class="highlight"><c- n>T</c-> <c- n>tmp</c-></code> from <code class="highlight"><c- n>il</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code> (which can throw),</p>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>unex</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
    <li data-md>
     <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>tmp</c-><c- p>)</c-></code> (which cannot throw) and</p>
    <li data-md>
     <p>set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>;</p>
   </ul>
   <p>otherwise</p>
   <ul>
    <li data-md>
     <p>move constructs an <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-> <c- n>tmp</c-></code> from <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- k>this</c-><c- o>-></c-><c- n>error</c-><c- p>())</c-></code> ,</p>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>unex</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
    <li data-md>
     <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>il</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code>. Either,</p>
     <ul>
      <li data-md>
       <p>the constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>, or</p>
      <li data-md>
       <p>the constructor did throw, so move-construct the <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>E</c-></code> is nothrow-move-constructible), and re-throw the exception.</p>
     </ul>
   </ul>
   <p><em>Ensures</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Returns:</em> A reference to the new contained value <code class="highlight"><c- n>val</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the operations specified in the effect clause.</p>
   <p><em>Remarks</em>: If an exception is thrown during the call to <code class="highlight"><c- n>T</c-></code>'s assignment nothing
changes.</p>
   <h3 class="heading settled" data-level="1.9" id="expected.object.swap"><span class="secno">1.9. </span><span class="content">�.�.4.4 Swap [<em>expected.object.swap</em>]</span><a class="self-link" href="#expected.object.swap"></a></h3>
<pre class="language-c++ highlight"><c- b>void</c-> <c- nf>swap</c-><c- p>(</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>>&amp;</c-> <c- n>rhs</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>:</p>
   <ul>
    <li data-md>
     <p>Lvalues of type <code class="highlight"><c- n>T</c-></code> are <code class="highlight"><c- n>Swappable</c-></code>; and</p>
    <li data-md>
     <p>Lvalues of type <code class="highlight"><c- n>E</c-></code> are <code class="highlight"><c- n>Swappable</c-></code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_void_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> or <code class="highlight"><c- n>is_void_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code> and either:</p>
     <ul>
      <li data-md>
       <p><code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>; or</p>
      <li data-md>
       <p><code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
     </ul>
   </ul>
   <p><em>Effects</em>: See Table <em>editor-please-pick-a-number-5</em></p>
   <table>
    <caption>Table <em>editor-please-pick-a-number-5</em> — <code class="highlight"><c- n>swap</c-><c- p>(</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>>&amp;</c-><c- p>)</c-></code> effects</caption>
    <tbody>
     <tr>
      <td>
      <td><code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>
      <td><code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>
     <tr>
      <td><code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>
      <td>if <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code> calls <code class="highlight"><c- k>using</c-> <c- n>std</c-><c- o>::</c-><c- n>swap</c-><c- p>;</c-> <c- n>swap</c-><c- p>(</c-><c- n>val</c-><c- p>,</c-> <c- n>rhs</c-><c- p>.</c-><c- n>val</c-><c- p>)</c-></code>
      <td>calls <code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>swap</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>
     <tr>
      <td><code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>
      <td>
       <ul>
        <li data-md>
         <p>if <code class="highlight"><c- n>T</c-></code> is <em>cv</em> <code class="highlight"><c- b>void</c-></code></p>
         <ul>
          <li data-md>
           <p>initializes <code class="highlight"><c- n>unex</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>rhs</c-><c- p>))</c-></code>. Either</p>
          <li data-md>
           <p>the constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">false</code>, destroys <code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code> set <code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>has_val</c-></code> to <code class="highlight">true</code>.</p>
          <li data-md>
           <p>the constructor did throw, rethrow the exception.</p>
         </ul>
        <li data-md>
         <p>otherwise if <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>,</p>
         <ul>
          <li data-md>
           <p>the <code class="highlight"><c- n>unex</c-></code> of <code class="highlight"><c- n>rhs</c-></code> is moved to a temporary variable <code class="highlight"><c- n>tmp</c-></code> of type <code class="highlight"><c- n>unexpected_type</c-></code>,</p>
          <li data-md>
           <p>followed by destruction of <code class="highlight"><c- n>unex</c-></code> as if by <code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
          <li data-md>
           <p><code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>val</c-></code> is direct-initialized from <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>. Either</p>
           <ul>
            <li data-md>
             <p>the constructor didn’t throw</p>
             <ul>
              <li data-md>
               <p>destroy <code class="highlight"><c- n>val</c-></code> as if by <code class="highlight"><c- k>this</c-><c- o>-></c-><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code>,</p>
              <li data-md>
               <p>the <code class="highlight"><c- n>unex</c-></code> of <code class="highlight"><c- k>this</c-></code> is direct-initialized from <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>tmp</c-><c- p>)</c-></code>, after this, <code class="highlight"><c- k>this</c-></code> does not contain a value; and <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>.</p>
             </ul>
            <li data-md>
             <p>the constructor did throw, so move-construct the <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>E</c-></code> is nothrow-move-constructible), and re-throw the exception.</p>
           </ul>
         </ul>
        <li data-md>
         <p>otherwise if <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>,</p>
         <ul>
          <li data-md>
           <p><code class="highlight"><c- n>val</c-></code> is moved to a temporary variable <code class="highlight"><c- n>tmp</c-></code> of type <code class="highlight"><c- n>T</c-></code>,</p>
          <li data-md>
           <p>followed by destruction of <code class="highlight"><c- n>val</c-></code> as if by <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code>,</p>
          <li data-md>
           <p>the <code class="highlight"><c- n>unex</c-></code> is direct-initialized from <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>other</c-><c- p>.</c-><c- n>error</c-><c- p>()))</c-></code>. Either</p>
           <ul>
            <li data-md>
             <p>the constructor didn’t throw</p>
             <ul>
              <li data-md>
               <p>destroy <code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>unexpect</c-></code> as if by <code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
              <li data-md>
               <p><code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>val</c-></code> is direct-initialized from <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>tmp</c-><c- p>)</c-></code>, after this, <code class="highlight"><c- k>this</c-></code> does not contain a value; and <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>.</p>
             </ul>
            <li data-md>
             <p>the constructor did throw, so move-construct the <code class="highlight"><c- n>T</c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>T</c-></code> is nothrow-move-constructible), and re-throw the exception.</p>
           </ul>
         </ul>
        <li data-md>
         <p>otherwise, the function is not defined.</p>
       </ul>
      <td>calls <code class="highlight"><c- k>using</c-> <c- n>std</c-><c- o>::</c-><c- n>swap</c-><c- p>;</c-> <c- n>swap</c-><c- p>(</c-><c- n>unexpect</c-><c- p>,</c-> <c- n>rhs</c-><c- p>.</c-><c- n>unexpect</c-><c- p>)</c-></code>
   </table>
   <p><em>Throws</em>: Any exceptions that the expressions in the Effects clause throw.</p>
   <p><em>Remarks</em>: The expression inside noexcept is equivalent to: <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_nothrow_swappable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_nothrow_swappable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <h3 class="heading settled" data-level="1.10" id="expected.object.observe"><span class="secno">1.10. </span><span class="content">�.�.4.5 Observers [<em>expected.object.observe</em>]</span><a class="self-link" href="#expected.object.observe"></a></h3>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>*</c-> <c- n>operator</c-><c- o>-></c-><c- p>()</c-> <c- k>const</c-><c- p>;</c->
<c- n>T</c-><c- o>*</c-> <c- n>operator</c-><c- o>-></c-><c- p>();</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code>.</p>
   <p><em>Expects</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Returns</em>: <code class="highlight"><c- n>addressof</c-><c- p>(</c-><c- n>val</c-><c- p>)</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>*</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
<c- n>T</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>*</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code>.</p>
   <p><em>Expects</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Returns</em>: <code class="highlight"><c- n>val</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>operator</c-><c- o>*</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
<c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>operator</c-><c- o>*</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;&amp;</c-><c- p>;</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code>.</p>
   <p><em>Expects</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Returns</em>: <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>val</c-><c- p>)</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- n>explicit</c-> <c- n>operator</c-> <c- nf>bool</c-><c- p>()</c-> <c- n>noexcept</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>has_val</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- b>bool</c-> <c- nf>has_value</c-><c- p>()</c-> <c- k>const</c-> <c- n>noexcept</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>has_val</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- b>void</c-> <c- n>expected</c-><c- o>&lt;</c-><c- b>void</c-><c- p>,</c-> <c- n>E</c-><c- o>>::</c-><c- n>value</c-><c- p>()</c-> <c- k>const</c-><c- p>;</c->
</pre>
   <p><em>Throws</em>: <code class="highlight"><c- n>bad_expected_access</c-><c- p>(</c-><c- n>error</c-><c- p>())</c-></code> if <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>expected</c-><c- o>::</c-><c- n>value</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
<c- n>constexpr</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>expected</c-><c- o>::</c-><c- n>value</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code>.</p>
   <p><em>Returns</em>: <code class="highlight"><c- n>val</c-></code>, if <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> .</p>
   <p><em>Throws</em>: <code class="highlight"><c- n>bad_expected_access</c-><c- p>(</c-><c- n>error</c-><c- p>())</c-></code> if <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>expected</c-><c- o>::</c-><c- n>value</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
<c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>expected</c-><c- o>::</c-><c- n>value</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;&amp;</c-><c- p>;</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>T</c-></code> is not <em>cv</em> <code class="highlight"><c- b>void</c-></code>.</p>
   <p><em>Returns</em>: <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>val</c-><c- p>)</c-></code>, if <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> .</p>
   <p><em>Throws</em>: <code class="highlight"><c- n>bad_expected_access</c-><c- p>(</c-><c- n>error</c-><c- p>())</c-></code> if <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- k>const</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
<c- n>constexpr</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
</pre>
   <p><em>Expects</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">false</code>.</p>
   <p><em>Returns</em>: <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- n>value</c-><c- p>()</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
<c- n>constexpr</c-> <c- k>const</c-> <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;&amp;</c-><c- p>;</c->
</pre>
   <p><em>Expects</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> is <code class="highlight">false</code>.</p>
   <p><em>Returns</em>: <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>unexpect</c-><c- p>.</c-><c- n>value</c-><c- p>())</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>T</c-> <c- n>value_or</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-> <c- n>v</c-><c- p>)</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-> <c- o>?</c-> <c- o>**</c-><c- k>this</c-> <c- o>:</c-> <c- k>static_cast</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>(</c-><c- n>v</c-><c- p>));</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>is_copy_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>and <code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code> the program is ill-formed.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>T</c-> <c- n>value_or</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-> <c- n>v</c-><c- p>)</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-> <c- o>?</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- o>**</c-><c- k>this</c-><c- p>)</c-> <c- o>:</c-> <c- k>static_cast</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>(</c-><c- n>v</c-><c- p>));</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code> the program is ill-formed.</p>
   <h3 class="heading settled" data-level="1.11" id="expected.equality_op"><span class="secno">1.11. </span><span class="content">�.�.4.6 Expected Equality operators [<em>expected.equality_op</em>]</span><a class="self-link" href="#expected.equality_op"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
    <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T2</c-><c- p>,</c-> <c- n>E2</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>);</c->
</pre>
   <p><em>Expects</em>: The expressions <code class="highlight"><c- o>*</c-><c- n>x</c-> <c- o>==</c-> <c- o>*</c-><c- n>y</c-></code> and <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-><c- o>==</c-> <c- n>y</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-></code> are well-formed and their results
are convertible to <code class="highlight"><c- b>bool</c-></code>.</p>
   <p><em>Returns</em>: If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- o>!=</c-> <c- b>bool</c-><c- p>(</c-><c- n>y</c-><c- p>)</c-></code>, <code class="highlight">false</code>; otherwise if <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- o>==</c-> false</code>, <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-> <c- o>==</c-> <c- n>y</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-></code>; otherwise <code class="highlight">true</code> if <code class="highlight"><c- n>T1</c-></code> and <code class="highlight"><c- n>T2</c-></code> are <em>cv</em> <code class="highlight"><c- b>void</c-></code> or <code class="highlight"><c- o>*</c-><c- n>x</c-> <c- o>==</c-> <c- o>*</c-><c- n>y</c-></code> otherwise.</p>
   <p><em>Remarks</em>: Specializations of this function template, for which <code class="highlight"><c- n>T1</c-></code> and <code class="highlight"><c- n>T2</c-></code> are <em>cv</em> <code class="highlight"><c- b>void</c-></code> or <code class="highlight"><c- o>*</c-><c- n>x</c-> <c- o>==</c-> <c- o>*</c-><c- n>y</c-></code> and <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-> <c- o>==</c-> <c- n>y</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-></code> is a core constant expression, are
constexpr functions.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
    <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T2</c-><c- p>,</c-> <c- n>E2</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>);</c->
</pre>
   <p><em>Mandates</em>: The expressions <code class="highlight"><c- o>*</c-><c- n>x</c-> <c- o>!=</c-> <c- o>*</c-><c- n>y</c-></code> and <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-> <c- o>!=</c-> <c- n>y</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-></code> are
well-formed and their results are convertible to <code class="highlight"><c- b>bool</c-></code>.</p>
   <p><em>Returns</em>: If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- o>!=</c-> <c- b>bool</c-><c- p>(</c-><c- n>y</c-><c- p>)</c-></code>, <code class="highlight">true</code>; otherwise if <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- o>==</c-> false</code>, <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-> <c- o>!=</c-> <c- n>y</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-></code>; otherwise <code class="highlight">true</code> if <code class="highlight"><c- n>T1</c-></code> and <code class="highlight"><c- n>T2</c-></code> are <em>cv</em> <code class="highlight"><c- b>void</c-></code> or <code class="highlight"><c- o>*</c-><c- n>x</c-> <c- o>!=</c-> <c- o>*</c-><c- n>y</c-></code>.</p>
   <p><em>Remarks</em>: Specializations of this function template, for which <code class="highlight"><c- n>T1</c-></code> and <code class="highlight"><c- n>T2</c-></code> are <em>cv</em> <code class="highlight"><c- b>void</c-></code> or <code class="highlight"><c- o>*</c-><c- n>x</c-> <c- o>!=</c-> <c- o>*</c-><c- n>y</c-></code> and <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-> <c- o>!=</c-> <c- n>y</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-></code> is a core
constant expression, are constexpr functions.</p>
   <h3 class="heading settled" data-level="1.12" id="expected.comparison_T"><span class="secno">1.12. </span><span class="content">�.�.4.7 Comparison with <code class="highlight"><c- n>T</c-></code> [<em>expected.comparison_T</em>]</span><a class="self-link" href="#expected.comparison_T"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- o>></c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-> <c- n>v</c-><c- p>);</c->
<c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- o>></c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-> <c- n>v</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>);</c->
</pre>
   <p><em>Mandates</em>: <code class="highlight"><c- n>T1</c-></code> and <code class="highlight"><c- n>T2</c-></code> are not <em>cv</em> <code class="highlight"><c- b>void</c-></code> and the expression <code class="highlight"><c- o>*</c-><c- n>x</c-> <c- o>==</c-> <c- n>v</c-></code> is well-formed
and its result is convertible to <code class="highlight"><c- b>bool</c-></code>. [ <em>Note:</em> <code class="highlight"><c- n>T1</c-></code> need not be <em>EqualityComparable</em>. - <em>end note</em>]</p>
   <p><em>Returns</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- o>?</c-> <c- o>*</c-><c- n>x</c-> <c- o>==</c-> <c- nl>v</c-> <c- p>:</c-> false<c- p>;</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- o>></c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-> <c- n>v</c-><c- p>);</c->
<c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- o>></c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-> <c- n>v</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>);</c->
</pre>
   <p><em>Mandates</em>: <code class="highlight"><c- n>T1</c-></code> and <code class="highlight"><c- n>T2</c-></code> are not <em>cv</em> <code class="highlight"><c- b>void</c-></code> and the expression <code class="highlight"><c- o>*</c-><c- n>x</c-> <c- o>==</c-> <c- n>v</c-></code> is well-formed
and its result is convertible to <code class="highlight"><c- b>bool</c-></code>. [ <em>Note:</em> <code class="highlight"><c- n>T1</c-></code> need not be <em>EqualityComparable</em>. - <em>end note</em>]</p>
   <p><em>Returns</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- o>?</c-> <c- o>*</c-><c- n>x</c-> <c- o>!=</c-> <c- nl>v</c-> <c- p>:</c-> false<c- p>;</c-></code>.</p>
   <h3 class="heading settled" data-level="1.13" id="expected.comparison_unexpected_E"><span class="secno">1.13. </span><span class="content">�.�.4.8 Comparison with <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> [<em>expected.comparison_unexpected_E</em>]</span><a class="self-link" href="#expected.comparison_unexpected_E"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-> <c- n>e</c-><c- p>);</c->
<c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-> <c- n>e</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>);</c->
</pre>
   <p><em>Mandates</em>: The expression <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-> <c- o>==</c-> <c- n>e</c-></code> is well-formed and
its result is convertible to <code class="highlight"><c- b>bool</c-></code>.</p>
   <p><em>Returns</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- o>?</c-> false <c- o>:</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-> <c- o>==</c-> <c- n>e</c-><c- p>;</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-> <c- n>e</c-><c- p>);</c->
<c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-> <c- n>e</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>);</c->
</pre>
   <p><em>Mandates</em>: The expression <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-> <c- o>!=</c-> <c- n>e</c-></code> is well-formed and
its result is convertible to <code class="highlight"><c- b>bool</c-></code>.</p>
   <p><em>Returns</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- o>?</c-> true <c- o>:</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-> <c- o>!=</c-> <c- n>e</c-><c- p>;</c-></code>.</p>
   <h3 class="heading settled" data-level="1.14" id="expected.specalg"><span class="secno">1.14. </span><span class="content">�.�.4.9 Specialized algorithms [<em>expected.specalg</em>]</span><a class="self-link" href="#expected.specalg"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- o>></c->
<c- b>void</c-> <c- n>swap</c-><c- p>(</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>noexcept</c-><c- p>(</c-><c- n>x</c-><c- p>.</c-><c- n>swap</c-><c- p>(</c-><c- n>y</c-><c- p>)));</c->
</pre>
   <p><em>Constraints</em>:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>T1</c-></code> is <em>cv</em> <code class="highlight"><c- b>void</c-></code> or <code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>T1</c-><c- o>></c-></code> is <code class="highlight">true</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_swappable_v</c-><c- o>&lt;</c-><c- n>T1</c-><c- o>></c-></code> is <code class="highlight">true</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>></c-></code> is <code class="highlight">true</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_swappable_v</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   </ul>
   <p><em>Effects</em>: Calls <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>swap</c-><c- p>(</c-><c- n>y</c-><c- p>)</c-></code>.</p>
   <h3 class="heading settled" data-level="1.15" id="expected.unexpected"><span class="secno">1.15. </span><span class="content">�.�.5 Unexpected objects [<em>expected.unexpected</em>]</span><a class="self-link" href="#expected.unexpected"></a></h3>
   <h3 class="heading settled" data-level="1.16" id="expected.unexpected.general"><span class="secno">1.16. </span><span class="content">�.�.5.1 General [<em>expected.unexpected.general</em>]</span><a class="self-link" href="#expected.unexpected.general"></a></h3>
   <p>This subclause describes class template <code class="highlight"><c- n>unexpected</c-></code> that
represents unexpected objects.</p>
   <h3 class="heading settled" data-level="1.17" id="expected.unexpected.object"><span class="secno">1.17. </span><span class="content">�.�.5.2 Class template <code class="highlight"><c- n>unexpected</c-></code> [<em>expected.unexpected.object</em>]</span><a class="self-link" href="#expected.unexpected.object"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>E</c-><c- o>></c->
<c- n>class</c-> <c- n>unexpected</c-> <c- p>{</c->
<c- nl>public</c-><c- p>:</c->
    <c- n>constexpr</c-> <c- n>unexpected</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&amp;</c-><c- p>)</c-> <c- o>=</c-> <c- k>default</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- nf>unexpected</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- o>=</c-> <c- k>default</c-><c- p>;</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>in_place_t</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>in_place_t</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>Err</c-><c- o>&amp;&amp;</c-><c- p>);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>explicit</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>)</c-> <c- n>unexpected</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>explicit</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>)</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;&amp;</c-><c- p>);</c->

    <c- n>constexpr</c-> <c- n>unexpected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&amp;</c-><c- p>)</c-> <c- o>=</c-> <c- k>default</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>unexpected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- o>=</c-> <c- k>default</c-><c- p>;</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>unexpected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>unexpected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;&amp;</c-><c- p>);</c->

    <c- n>constexpr</c-> <c- k>const</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-> <c- n>noexcept</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- o>&amp;</c-> <c- n>noexcept</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- k>const</c-> <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;&amp;</c-> <c- n>noexcept</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- o>&amp;&amp;</c-> <c- n>noexcept</c-><c- p>;</c->

    <c- b>void</c-> <c- nf>swap</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&amp;</c-> <c- n>other</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->

    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
        <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c->
        <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
        <c- n>constexpr</c-> <c- b>bool</c->
        <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-><c- p>);</c->

    <c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>E1</c-><c- o>></c->
    <c- n>friend</c-> <c- b>void</c-> <c- n>swap</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>noexcept</c-><c- p>(</c-><c- n>x</c-><c- p>.</c-><c- n>swap</c-><c- p>(</c-><c- n>y</c-><c- p>)));</c->

<c- nl>private</c-><c- p>:</c->
    <c- n>E</c-> <c- n>val</c-><c- p>;</c-> <c- c1>// exposition only</c->
<c- p>};</c->

<c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>E</c-><c- o>></c-> <c- n>unexpected</c-><c- p>(</c-><c- n>E</c-><c- p>)</c-> <c- o>-></c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>;</c->
</pre>
   <p>A program that instantiates the definition of <code class="highlight"><c- n>unexpected</c-></code> for a non-object
type, an array type, a specialization of <code class="highlight"><c- n>unexpected</c-></code> or an cv-qualified type is
ill-formed.</p>
   <h4 class="heading settled" data-level="1.17.1" id="expected.unexpected.ctor"><span class="secno">1.17.1. </span><span class="content">�.�.5.2.1 Constructors [<em>expected.unexpected.ctor</em>]</span><a class="self-link" href="#expected.unexpected.ctor"></a></h4>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>Err</c-><c- o>&amp;&amp;</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>Err</c-><c- o>></c-></code> is <code class="highlight">true</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_same_v</c-><c- o>&lt;</c-><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>,</c-> <c- n>in_place_t</c-><c- o>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_same_v</c-><c- o>&lt;</c-><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>,</c-> <c- n>unexpected</c-><c- o>></c-></code> is <code class="highlight">false</code>.</p>
   </ul>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an
object of type <code class="highlight"><c- n>E</c-></code> with the expression <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>></c-><c- p>(</c-><c- n>e</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>E</c-></code>’s selected constructor is a constant subexpression, this
constructor is a constexpr constructor.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>in_place_t</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>Args</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an
object of type <code class="highlight"><c- n>E</c-></code> with the arguments <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>:
If <code class="highlight"><c- n>E</c-></code>’s selected constructor is a constant subexpression, this constructor is a constexpr constructor.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>in_place_t</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>Args</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an
object of type <code class="highlight"><c- n>E</c-></code> with the arguments <code class="highlight"><c- n>il</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>:
If <code class="highlight"><c- n>E</c-></code>’s selected constructor is a constant subexpression, this constructor is a constexpr constructor.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-><c- o>></c->
<c- n>constexpr</c-> <c- n>explicit</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>)</c-> <c- n>unexpected</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- k>const</c-> <c- n>Err</c-><c- o>&amp;></c-></code> is <code class="highlight">true</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>></c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>></c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>.</p>
   </ul>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an
object of type <code class="highlight"><c- n>E</c-></code> with the expression <code class="highlight"><c- n>e</c-><c- p>.</c-><c- n>val</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>: The expression inside <code class="highlight"><c- k>explicit</c-></code> is equivalent to <code class="highlight"><c- o>!</c-><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>Err</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-><c- o>></c->
<c- n>constexpr</c-> <c- n>explicit</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>)</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;&amp;</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>Err</c-><c- o>></c-></code> is <code class="highlight">true</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>></c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>; and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>></c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>.</p>
   </ul>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an
object of type <code class="highlight"><c- n>E</c-></code> with the expression <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>e</c-><c- p>.</c-><c- n>val</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>: The expression inside <code class="highlight"><c- k>explicit</c-></code> is equivalent to <code class="highlight"><c- o>!</c-><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>Err</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code>.</p>
   <h4 class="heading settled" data-level="1.17.2" id="expected.unexpected.assign"><span class="secno">1.17.2. </span><span class="content">�.�.5.2.2 Assignment [<em>expected.unexpected.assign</em>]</span><a class="self-link" href="#expected.unexpected.assign"></a></h4>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>unexpected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>is_assignable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- k>const</c-> <c- n>Err</c-><c- o>&amp;></c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Effects</em>: Equivalent to <code class="highlight"><c- n>val</c-> <c- o>=</c-> <c- n>e</c-><c- p>.</c-><c- n>val</c-></code>.</p>
   <p><em>Returns</em>: <code class="highlight"><c- o>*</c-><c- k>this</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>E</c-></code>’s selected assignment operator is a constant subexpression,
this function is a constexpr function.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>unexpected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;&amp;</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>is_assignable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>Err</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Effects</em>: Equivalent to <code class="highlight"><c- n>val</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>e</c-><c- p>.</c-><c- n>val</c-><c- p>)</c-></code>.</p>
   <p><em>Returns</em>: <code class="highlight"><c- o>*</c-><c- k>this</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>E</c-></code>’s selected assignment operator is a constant subexpression,
this function is a constexpr function.</p>
   <h4 class="heading settled" data-level="1.17.3" id="expected.unexpected.observe"><span class="secno">1.17.3. </span><span class="content">�.�.5.2.3 Observers [<em>expected.unexpected.observe</em>]</span><a class="self-link" href="#expected.unexpected.observe"></a></h4>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- k>const</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
<c- n>constexpr</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>val</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
<c- n>constexpr</c-> <c- k>const</c-> <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;&amp;</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>val</c-><c- p>)</c-></code>.</p>
   <h4 class="heading settled" data-level="1.17.4" id="expected.unexpected.swap"><span class="secno">1.17.4. </span><span class="content">�.�.5.2.4 Swap [<em>expected.unexpected.ctor</em>]</span><a class="self-link" href="#expected.unexpected.swap"></a></h4>
<pre class="language-c++ highlight"><c- b>void</c-> <c- nf>swap</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&amp;</c-> <c- n>other</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->
</pre>
   <p><em>Mandates</em>: <code class="highlight"><c- n>is_swappable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Effects</em>: Equivalent to <code class="highlight"><c- k>using</c-> <c- n>std</c-><c- o>::</c-><c- n>swap</c-><c- p>;</c-> <c- n>swap</c-><c- p>(</c-><c- n>val</c-><c- p>,</c-> <c- n>other</c-><c- p>.</c-><c- n>val</c-><c- p>);</c-></code>.</p>
   <p><em>Throws</em>: Any exceptions thrown by the operations in the relevant part of [<strong>expected.swap</strong>].</p>
   <p><em>Remarks</em>: The expression inside <code class="highlight"><c- k>noexcept</c-></code> is equivalent to: <code class="highlight"><c- n>is_nothrow_swappable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <h3 class="heading settled" data-level="1.18" id="expected.unexpected.equality_op"><span class="secno">1.18. </span><span class="content">�.�.5.2.5 Equality operators [<em>expected.unexpected.equality_op</em>]</span><a class="self-link" href="#expected.unexpected.equality_op"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
    <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>);</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>value</c-><c- p>()</c-> <c- o>==</c-> <c- n>y</c-><c- p>.</c-><c- n>value</c-><c- p>()</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
    <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>);</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>value</c-><c- p>()</c-> <c- o>!=</c-> <c- n>y</c-><c- p>.</c-><c- n>value</c-><c- p>()</c-></code>.</p>
   <h4 class="heading settled" data-level="1.18.1" id="expected.unexpected.specalg"><span class="secno">1.18.1. </span><span class="content">�.�.5.2.5 Specialized algorithms [<em>expected.unexpected.specalg</em>]</span><a class="self-link" href="#expected.unexpected.specalg"></a></h4>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>E1</c-><c- o>></c->
    <c- n>friend</c-> <c- b>void</c-> <c- n>swap</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>noexcept</c-><c- p>(</c-><c- n>x</c-><c- p>.</c-><c- n>swap</c-><c- p>(</c-><c- n>y</c-><c- p>)));</c->
</pre>
   <p><em>Constraints</em>: <code class="highlight"><c- n>is_swappable_v</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <p><em>Effects</em>: Equivalent to <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>swap</c-><c- p>(</c-><c- n>y</c-><c- p>)</c-></code>.</p>
   <h3 class="heading settled" data-level="1.19" id="expected.bad_expected_access"><span class="secno">1.19. </span><span class="content">�.�.6 Template Class <code class="highlight"><c- n>bad_expected_access</c-></code> [<em>expected.bad_expected_access</em>]</span><a class="self-link" href="#expected.bad_expected_access"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;</c-><c- n>class</c-> <c- n>E</c-><c- o>></c->
<c- n>class</c-> <c- nl>bad_expected_access</c-> <c- p>:</c-> <c- n>public</c-> <c- n>bad_expected_access</c-><c- o>&lt;</c-><c- b>void</c-><c- o>></c-> <c- p>{</c->
<c- nl>public</c-><c- p>:</c->
    <c- n>explicit</c-> <c- n>bad_expected_access</c-><c- p>(</c-><c- n>E</c-><c- p>);</c->
    <c- n>virtual</c-> <c- k>const</c-> <c- b>char</c-><c- o>*</c-> <c- nf>what</c-><c- p>()</c-> <c- k>const</c-> <c- n>noexcept</c-> <c- n>override</c-><c- p>;</c->
    <c- n>E</c-><c- o>&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
    <c- k>const</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
    <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
    <c- k>const</c-> <c- n>E</c-><c- o>&amp;&amp;</c->  <c- n>error</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;&amp;</c-><c- p>;</c->
<c- nl>private</c-><c- p>:</c->
    <c- n>E</c-> <c- n>val</c-><c- p>;</c-> <c- c1>// exposition only</c->
<c- p>};</c->
</pre>
   <p class="issue" id="issue-1727f25d"><a class="self-link" href="#issue-1727f25d"></a> Wondering if we just need a <code class="highlight"><c- k>const</c-><c- o>&amp;</c-></code> overload as we do for <code class="highlight"><c- n>system_error</c-></code>.</p>
   <p>The template class <code class="highlight"><c- n>bad_expected_access</c-></code> defines the type of objects thrown as
exceptions to report the situation where an attempt is made to access the value
of <code class="highlight"><c- n>expected</c-></code> object that contains an <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>.</p>
<pre class="language-c++ highlight"><c- n>bad_expected_access</c-><c- o>::</c-><c- n>bad_expected_access</c-><c- p>(</c-><c- n>E</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>val</c-></code> with <code class="highlight"><c- n>e</c-></code>.</p>
   <p><em>Ensures</em>: <code class="highlight"><c- n>what</c-><c- p>()</c-></code> returns an implementation-defined NTBS.</p>
<pre class="language-c++ highlight"><c- k>const</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
<c- n>E</c-><c- o>&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>val</c-><c- p>;</c-></code></p>
<pre class="language-c++ highlight"><c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
<c- k>const</c-> <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;&amp;</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>val</c-><c- p>);</c-></code></p>
<pre class="language-c++ highlight"><c- n>virtual</c-> <c- k>const</c-> <c- b>char</c-><c- o>*</c-> <c- nf>what</c-><c- p>()</c-> <c- k>const</c-> <c- n>noexcept</c-> <c- n>override</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: An implementation-defined NTBS.</p>
   <h3 class="heading settled" data-level="1.20" id="expected.bad_expected_access_base"><span class="secno">1.20. </span><span class="content">�.�.7 Class <code class="highlight"><c- n>bad_expected_access</c-><c- o>&lt;</c-><c- b>void</c-><c- o>></c-></code> [<em>expected.bad_expected_access_base</em>]</span><a class="self-link" href="#expected.bad_expected_access_base"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-><c- o>&lt;></c->
<c- n>class</c-> <c- n>bad_expected_access</c-><c- o>&lt;</c-><c- b>void</c-><c- o>></c-> <c- o>:</c-> <c- n>public</c-> <c- n>exception</c-> <c- p>{</c->
<c- nl>public</c-><c- p>:</c->
    <c- n>explicit</c-> <c- n>bad_expected_access</c-><c- p>();</c->
<c- p>};</c->
</pre>
   <h3 class="heading settled" data-level="1.21" id="expected.unexpect"><span class="secno">1.21. </span><span class="content">�.�.8 <code class="highlight"><c- n>unexpect</c-></code> tag [<em>expected.unexpect</em>]</span><a class="self-link" href="#expected.unexpect"></a></h3>
<pre class="highlight"><code class="highlight"><c- k><c- k>struct</c-></c-> <c- nf><c- nf>unexpect_t</c-></c-><c- p><c- p>(</c-></c-><i><c- n><c- n>see</c-></c-> <c- n><c- n>below</c-></c-></i><c- p><c- p>);</c-></c->
<c- kr><c- kr>inline</c-></c-> <c- k><c- k>constexpr</c-></c-> <c- n><c- n>unexpect_t</c-></c-> <c- nf><c- nf>unexpect</c-></c-><c- p><c- p>(</c-></c-><i><c- n><c- n>unspecified</c-></c-></i><c- p><c- p>);</c-></c->
</code></pre>
   <p>Type <code class="highlight"><c- n>unexpect_t</c-></code> does not have a default constructor or an initializer-list
constructor, and is not an aggregate.</p>
   <h2 class="heading settled" data-level="2" id="qq"><span class="secno">2. </span><span class="content">Open Questions</span><a class="self-link" href="#qq"></a></h2>
   <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>expected</c-></code> is a vocabulary type with an opinionated design and a proven
record under varied forms in a multitude of codebases. Its current form has
undergone multiple revisions and received substantial feedback, falling roughly
in the following categories:</p>
   <ol>
    <li data-md>
     <p><strong>Ergonomics</strong>: is this <em>the right way</em> to expose such functionality?</p>
    <li data-md>
     <p><strong>Disappointment</strong>: should we expose this in the Standard, given C++'s
 existing error handling mechanisms?</p>
    <li data-md>
     <p><strong>STL usage</strong>: should the Standard Template Library adopt this class, at
 which pace, and where?</p>
   </ol>
   <p>LEWG and EWG have nonetheless reached consensus that a class of this general
approach is probably desirable, and the only way to truly answer these questions
is to try it out in a TS and ask for explicit feedback from developers. The
authors hope that developers will provide new information which they’ll be able
to communicate to the Committee.</p>
   <p>Here are open questions, and questions which the Committee thinks are settled
and which new information can justify revisiting.</p>
   <h3 class="heading settled" data-level="2.1" id="ergo"><span class="secno">2.1. </span><span class="content">Ergonomics</span><a class="self-link" href="#ergo"></a></h3>
   <ol>
    <li data-md>
     <p>Name:</p>
     <ul>
      <li data-md>
       <p>Is <code class="highlight"><c- n>expected</c-></code> the right name?</p>
      <li data-md>
       <p>Does it express intent both as a consumer and a producer?</p>
     </ul>
    <li data-md>
     <p>Is <code class="highlight"><c- n>E</c-></code> a salient property of <code class="highlight"><c- n>expected</c-></code>?</p>
    <li data-md>
     <p>Is <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- b>void</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> clear on what it expresses as a return type?</p>
    <li data-md>
     <p>Would it make sense for <code class="highlight"><c- n>expected</c-></code> to support containing <em>both</em> <code class="highlight"><c- n>T</c-></code> and <code class="highlight"><c- n>E</c-></code> (in some designs, either one of them being optional), or is this use case better handled by a separate proposal?</p>
    <li data-md>
     <p>Is the order of parameters <code class="highlight"><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> appropriate?</p>
    <li data-md>
     <p>Is usage of <code class="highlight"><c- n>expected</c-></code> "viral" in a codebase, or can it be adopted incrementally?</p>
    <li data-md>
     <ul>
      <li data-md>
       <p>Missing <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-><c- n>E</c-><c- o>>::</c-><c- n>emplace</c-></code> for <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>.</p>
      <li data-md>
       <p>The in-place construction from a <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> using the <code class="highlight"><c- n>unexpet</c-></code> tag doesn’t conveys the in-place nature of this constructor.</p>
      <li data-md>
       <p>Do we need in-place using indexes, as variant?</p>
     </ul>
    <li data-md>
     <p>Comparisons:</p>
     <ul>
      <li data-md>
       <p>Are <code class="highlight"><c- o>==</c-></code> and <code class="highlight"><c- o>!=</c-></code> useful?</p>
      <li data-md>
       <p>Should other comparisons be provided?</p>
      <li data-md>
       <p>What usages of <code class="highlight"><c- n>expected</c-></code> mandate putting instances in a <code class="highlight"><c- n>map</c-></code>, or other such container?</p>
      <li data-md>
       <p>Should <code class="highlight"><c- n>hash</c-></code> be provided?</p>
      <li data-md>
       <p>What usages of <code class="highlight"><c- n>expected</c-></code> mandate putting instances in an <code class="highlight"><c- n>unordered_map</c-></code>, or other such container?</p>
      <li data-md>
       <p>Should <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> always be comparable if <code class="highlight"><c- n>T</c-></code> is comparable, even if <code class="highlight"><c- n>E</c-></code> is not comparable?</p>
     </ul>
    <li data-md>
     <p>Error type <code class="highlight"><c- n>E</c-></code>:</p>
     <ul>
      <li data-md>
       <p>Have <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- b>void</c-><c- o>></c-></code> and <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- b>void</c-><c- o>></c-></code> a sense?</p>
      <li data-md>
       <p><code class="highlight"><c- n>E</c-></code> template parameter has no default. Should it?</p>
      <li data-md>
       <p>Should <code class="highlight"><c- n>expected</c-></code> be specialized for particular <code class="highlight"><c- n>E</c-></code> types such as <code class="highlight"><c- n>exception_ptr</c-></code> and how?</p>
      <li data-md>
       <p>Should <code class="highlight"><c- n>expected</c-></code> handle <code class="highlight"><c- n>E</c-></code> types with a built-in "success" value any differently and how?</p>
      <li data-md>
       <p><code class="highlight"><c- n>expected</c-></code> is not implicitly constructible from an <code class="highlight"><c- n>E</c-></code>, even when unambiguous from <code class="highlight"><c- n>T</c-></code>, because as a vocabulary type it wants unexpected error construction to be verbose, and require hopping through an <code class="highlight"><c- n>unexpected</c-></code>. Is the verbosity extraneous? We could alleviate the verbosity by adding a <code class="highlight"><c- p>.</c-><c- n>unexpected</c-><c- p>()</c-></code> method to <code class="highlight"><c- n>expected</c-></code>, so that one doesn’t have to write <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>e</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code> when constructing a new <code class="highlight"><c- n>expected</c-></code> from an error.</p>
     </ul>
    <li data-md>
     <p>Does usage of this class cause a meaningful performance impact compared to using error codes?</p>
    <li data-md>
     <p>The accessor design offers a terse unchecked dereference operator (expected to be used alongside the implicit <code class="highlight"><c- b>bool</c-></code> conversion), as well as <code class="highlight"><c- n>value</c-><c- p>()</c-></code> and <code class="highlight"><c- n>error</c-><c- p>()</c-></code> accessors which are checked. Is that a gotcha, or is it similar enough to classes such as <code class="highlight"><c- n>optional</c-></code> to be unsurprising?</p>
    <li data-md>
     <p>Is <code class="highlight"><c- n>bad_expected_access</c-></code> the right thing to throw?</p>
    <li data-md>
     <p>Should some members be <code class="highlight"><c- n>nodiscard</c-></code>?</p>
    <li data-md>
     <p>Should constructors of <code class="highlight"><c- n>expected</c-></code> disallow <code class="highlight"><c- n>T</c-></code> which are specializations of <code class="highlight"><c- n>expected</c-></code>?</p>
    <li data-md>
     <p>Similarly, can <code class="highlight"><c- n>T</c-></code> and <code class="highlight"><c- n>E</c-></code> be abominable functions?</p>
   </ol>
   <h3 class="heading settled" data-level="2.2" id="dis"><span class="secno">2.2. </span><span class="content">Disappointment</span><a class="self-link" href="#dis"></a></h3>
   <p>C++ already supports exceptions and error codes, <code class="highlight"><c- n>expected</c-></code> would be a third
kind of error handling.</p>
   <ol>
    <li data-md>
     <p>where does <code class="highlight"><c- n>expected</c-></code> work better than either exceptions or error handling?</p>
    <li data-md>
     <p><code class="highlight"><c- n>expected</c-></code> was designed to be particularly well suited to APIs which require their immediate caller to consider an error scenario. Do it succeed in that purpose?</p>
    <li data-md>
     <p>Do codebases successfully compose these three types of error handling?</p>
    <li data-md>
     <p>Is debuggability any harder?</p>
    <li data-md>
     <p>Is it easy to teach C++ as a whole with a third type of error handling?</p>
   </ol>
   <h3 class="heading settled" data-level="2.3" id="stl"><span class="secno">2.3. </span><span class="content">STL Usage</span><a class="self-link" href="#stl"></a></h3>
   <ol>
    <li data-md>
     <p>Should <code class="highlight"><c- n>expected</c-></code> be used in the STL at the same time as it gets standardized?</p>
    <li data-md>
     <p>Where, considering <code class="highlight"><c- n>std2</c-></code> may be a good place to change APIs?</p>
   </ol>
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  <h2 class="no-num no-ref heading settled" id="references"><span class="content">References</span><a class="self-link" href="#references"></a></h2>
  <h3 class="no-num no-ref heading settled" id="informative"><span class="content">Informative References</span><a class="self-link" href="#informative"></a></h3>
  <dl>
   <dt id="biblio-n4015">[N4015]
   <dd>V. Escriba, P. Talbot. <a href="https://wg21.link/n4015">A proposal to add a utility class to represent expected monad</a>. 26 May 2014. URL: <a href="https://wg21.link/n4015">https://wg21.link/n4015</a>
   <dt id="biblio-p0323r4">[P0323r4]
   <dd>Vicente Botet, JF Bastien. <a href="https://wg21.link/p0323r4">std::expected</a>. 26 November 2017. URL: <a href="https://wg21.link/p0323r4">https://wg21.link/p0323r4</a>
   <dt id="biblio-p0323r5">[P0323r5]
   <dd>Vicente Botet, JF Bastien. <a href="https://wg21.link/p0323r5">std::expected</a>. 8 February 2018. URL: <a href="https://wg21.link/p0323r5">https://wg21.link/p0323r5</a>
   <dt id="biblio-p0323r6">[P0323r6]
   <dd>Vicente Botet, JF Bastien. <a href="https://wg21.link/p0323r6">std::expected</a>. 2 April 2018. URL: <a href="https://wg21.link/p0323r6">https://wg21.link/p0323r6</a>
  </dl>
  <h2 class="no-num no-ref heading settled" id="issues-index"><span class="content">Issues Index</span><a class="self-link" href="#issues-index"></a></h2>
  <div style="counter-reset:issue">
   <div class="issue"> Wondering if we just need a <code class="highlight"><c- k>const</c-><c- o>&amp;</c-></code> overload as we do for <code class="highlight"><c- n>system_error</c-></code>.<a href="#issue-1727f25d"> ↵ </a></div>
  </div>